[dart_tooling_mcp_server] add get_widget_tree tool

[kenzieschmoll]

This PR adds a tool that gets the widget tree for a running Flutter app. In its current form, this tool calls the ext.flutter.inspector.getRootWidgetTree service extensions with the following parameters:

'groupName': groupId,
'isSummaryTree': 'true',
'withPreviews': 'true',
'fullDetails': 'true',

This will return Widgets that were added to the tree from the user's code (it will not contain implementation widgets). @elliette what do you think of these default values?

Example response:

{description: [root], type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-83, locationId: 0, creationLocation: {file: file:///Users/kenzieschmoll/develop/flutter/packages/flutter/lib/src/widgets/binding.dart, line: 1331, column: 24, name: RootWidget}, children: [{description: MyApp, type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-84, locationId: 1, creationLocation: {file: file:///Users/kenzieschmoll/develop/dart-lang/ai/pkgs/dart_tooling_mcp_server/test_fixtures/counter_app/lib/main.dart, line: 8, column: 16, name: MyApp}, createdByLocalProject: true, children: [{description: MaterialApp, type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-85, locationId: 2, creationLocation: {file: file:///Users/kenzieschmoll/develop/dart-lang/ai/pkgs/dart_tooling_mcp_server/test_fixtures/counter_app/lib/main.dart, line: 16, column: 12, name: MaterialApp}, createdByLocalProject: true, children: [{description: MyHomePage, type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-86, locationId: 3, creationLocation: {file: file:///Users/kenzieschmoll/develop/dart-lang/ai/pkgs/dart_tooling_mcp_server/test_fixtures/counter_app/lib/main.dart, line: 21, column: 19, name: MyHomePage}, createdByLocalProject: true, children: [{description: Scaffold, type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-87, locationId: 4, creationLocation: {file: file:///Users/kenzieschmoll/develop/dart-lang/ai/pkgs/dart_tooling_mcp_server/test_fixtures/counter_app/lib/main.dart, line: 46, column: 12, name: Scaffold}, createdByLocalProject: true, children: [{description: Center, type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-88, locationId: 5, creationLocation: {file: file:///Users/kenzieschmoll/develop/dart-lang/ai/pkgs/dart_tooling_mcp_server/test_fixtures/counter_app/lib/main.dart, line: 51, column: 13, name: Center}, createdByLocalProject: true, children: [{description: Column, type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-89, locationId: 6, creationLocation: {file: file:///Users/kenzieschmoll/develop/dart-lang/ai/pkgs/dart_tooling_mcp_server/test_fixtures/counter_app/lib/main.dart, line: 52, column: 16, name: Column}, createdByLocalProject: true, children: [{description: Row, type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-47, locationId: 7, creationLocation: {file: file:///Users/kenzieschmoll/develop/dart-lang/ai/pkgs/dart_tooling_mcp_server/test_fixtures/counter_app/lib/main.dart, line: 55, column: 19, name: Row}, createdByLocalProject: true, children: [{description: Text, type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-90, locationId: 8, creationLocation: {file: file:///Users/kenzieschmoll/develop/dart-lang/ai/pkgs/dart_tooling_mcp_server/test_fixtures/counter_app/lib/main.dart, line: 57, column: 17, name: Text}, createdByLocalProject: true, textPreview: You have pushed the button this many times:, children: [], widgetRuntimeType: Text, stateful: false}, {description: Text, type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-91, locationId: 9, creationLocation: {file: file:///Users/kenzieschmoll/develop/dart-lang/ai/pkgs/dart_tooling_mcp_server/test_fixtures/counter_app/lib/main.dart, line: 58, column: 17, name: Text}, createdByLocalProject: true, textPreview: And this Row should create an overflow error because it contains way more text than could ever fit on a single Row on both a mobile app or the default size of a desktop app., children: [], widgetRuntimeType: Text, stateful: false}], widgetRuntimeType: Row, stateful: false}, {description: Text, type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-92, locationId: 10, creationLocation: {file: file:///Users/kenzieschmoll/develop/dart-lang/ai/pkgs/dart_tooling_mcp_server/test_fixtures/counter_app/lib/main.dart, line: 65, column: 13, name: Text}, createdByLocalProject: true, textPreview: 0, children: [], widgetRuntimeType: Text, stateful: false}], widgetRuntimeType: Column, stateful: false}], widgetRuntimeType: Center, stateful: false}, {description: AppBar, type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-93, locationId: 11, creationLocation: {file: file:///Users/kenzieschmoll/develop/dart-lang/ai/pkgs/dart_tooling_mcp_server/test_fixtures/counter_app/lib/main.dart, line: 47, column: 15, name: AppBar}, createdByLocalProject: true, children: [{description: Text, type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-94, locationId: 12, creationLocation: {file: file:///Users/kenzieschmoll/develop/dart-lang/ai/pkgs/dart_tooling_mcp_server/test_fixtures/counter_app/lib/main.dart, line: 49, column: 16, name: Text}, createdByLocalProject: true, textPreview: Flutter Demo Home Page, children: [], widgetRuntimeType: Text, stateful: false}], widgetRuntimeType: AppBar, stateful: true}, {description: FloatingActionButton, type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-95, locationId: 13, creationLocation: {file: file:///Users/kenzieschmoll/develop/dart-lang/ai/pkgs/dart_tooling_mcp_server/test_fixtures/counter_app/lib/main.dart, line: 72, column: 29, name: FloatingActionButton}, createdByLocalProject: true, children: [{description: Icon, type: _ElementDiagnosticableTreeNode, style: dense, hasChildren: true, allowWrap: false, summaryTree: true, valueId: inspector-96, locationId: 14, creationLocation: {file: file:///Users/kenzieschmoll/develop/dart-lang/ai/pkgs/dart_tooling_mcp_server/test_fixtures/counter_app/lib/main.dart, line: 75, column: 22, name: Icon}, createdByLocalProject: true, children: [], widgetRuntimeType: Icon, stateful: false}], widgetRuntimeType: FloatingActionButton, stateful: false}], widgetRuntimeType: Scaffold, stateful: true}], widgetRuntimeType: MyHomePage, stateful: true}], widgetRuntimeType: MaterialApp, stateful: true}], widgetRuntimeType: MyApp, stateful: false}], widgetRuntimeType: RootWidget, stateful: false}

See https://github.com/flutter/flutter/blob/master/packages/flutter/lib/src/widgets/service_extensions.dart/#L126 for other Widget Inspector service extensions we may be interested in exposing. It is possible that getDetailsSubtree could be a better candidate for a getting a smaller portion of the widget tree (for example getting the subtree of a widget referenced in a Flutter error).

[kenzieschmoll]

@elliette is cleaning up this object group necessary? Or do you think we should re-use this object group for all uses of this tool and clean up when the server gets shut down? I'm not super familiar with why we use these object groups in the Inspector.

[elliette]

Hmm I'm also not familiar with the object group lifecycle. I see this comment: https://github.com/flutter/flutter/blob/296df33be866d0cd8387524e288d9b280e725795/packages/flutter/lib/src/widgets/widget_inspector.dart#L924-L927

But I'm not sure if how we should be creating / disposing object groups is documented anywhere. I need to do more investigation

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[elliette]

Depending on how we expect this to be used, I'm not sure if fullDetails is necessary.

fullDetails returns a substantially larger tree: flutter/flutter#157309

All the information we need to display the tree in DevTools is available without fullDetails. We only set fullDetails to true when requesting an individual node in the tree.