[browser] Support WasmFilesToIncludeInFileSystem in WasmSdk

[maraf]

Use WasmFilesToIncludeInFileSystem items to automatically load files to VFS when the application is starting.

The identity of WasmFilesToIncludeInFileSystem needs to be a relative path to files in wwwroot (either physical or linked). The optional TargetPath metadata allows to modify file location in VFS. If the metadata is omitted, a default location will be resolved from relative file path in wwwroot.

Example:

• Having a wwwroot/file.txt file
  • <WasmFilesToIncludeInFileSystem Include="file.txt" /> will load the file to /file.txt
  • <WasmFilesToIncludeInFileSystem Include="file.txt" TargetPath="/mydata/file.txt" /> will load the file to /mydata/file.txt
• Having a wwwroot/subdir/file.txt file
  • <WasmFilesToIncludeInFileSystem Include="subdir/file.txt" /> will load the file to /subdir/file.txt
  • <WasmFilesToIncludeInFileSystem Include="subdir/file.txt" TargetPath="/mydata/file.txt" /> will load the file to /mydata/file.txt

When `WasmFilesToIncludeInFileSystem` item is missing in StaticWebAssets, build fails (example output)

/workspaces/runtime/artifacts/bin/Wasm.Build.Tests/Debug/net10.0/linux-x64/wbtartifacts/nuget/SatelliteLoadingTestsFromReference_Release_False_st4zw1nv_xij/microsoft.net.sdk.webassembly.pack/10.0.0-dev/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets(353,5): error : Some of the 'WasmFilesToIncludeInFileSystem' where not found in StaticWebAssets. WasmFilesToIncludeInFileSystem: Vfs1.txt;subdir/Vfs2.txt;subdir/subsubdir/Vfs3.txt;NonExistent.txt, matched StaticWebAssets: /workspaces/runtime/artifacts/bin/Wasm.Build.Tests/Debug/net10.0/linux-x64/wbtartifacts/SatelliteLoadingTestsFromReference_Release_False_st4zw1nv_xij/App/wwwroot/Vfs1.txt;/workspaces/runtime/artifacts/bin/Wasm.Build.Tests/Debug/net10.0/linux-x64/wbtartifacts/SatelliteLoadingTestsFromReference_Release_False_st4zw1nv_xij/App/wwwroot/subdir/Vfs2.txt;/workspaces/runtime/artifacts/bin/Wasm.Build.Tests/Debug/net10.0/linux-x64/wbtartifacts/SatelliteLoadingTestsFromReference_Release_False_st4zw1nv_xij/App/wwwroot/subdir/subsubdir/Vfs3.txt [/workspaces/runtime/artifacts/bin/Wasm.Build.Tests/Debug/net10.0/linux-x64/wbtartifacts/SatelliteLoadingTestsFromReference_Release_False_st4zw1nv_xij/App/WasmBasicTestApp.csproj]

Fixes #99223

[Copilot]

Pull Request Overview

This PR implements support for automatically loading files into the WebAssembly Virtual File System (VFS) using the WasmFilesToIncludeInFileSystem item in the WasmSdk. Files specified with this item are loaded into VFS at application startup, with support for custom target paths via TargetPath metadata.

Key Changes:

• Added VFS resource support in boot JSON generation to handle files marked with vfs: trait
• Updated bundler-friendly mode to correctly reference VFS assets with relative paths
• Implemented target path resolution with fallback to file's wwwroot relative path

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/tasks/WasmAppBuilder/WasmAppBuilder.cs	Updated virtual path prefix to respect RuntimeAssetsLocation
src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/GenerateWasmBootJson.cs	Added VFS resource handling in boot config generation
src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/BootJsonBuilderHelper.cs	Fixed VFS asset path generation for bundler-friendly mode
src/mono/wasm/testassets/WasmBasicTestApp/App/wwwroot/subdir/subsubdir/Vfs3.txt	Test file for nested VFS path without custom TargetPath
src/mono/wasm/testassets/WasmBasicTestApp/App/wwwroot/subdir/Vfs2.txt	Test file for VFS with custom TargetPath
src/mono/wasm/testassets/WasmBasicTestApp/App/wwwroot/main.js	Added test scenario entry point
src/mono/wasm/testassets/WasmBasicTestApp/App/wwwroot/Vfs1.txt	Test file for root-level VFS with custom TargetPath
src/mono/wasm/testassets/WasmBasicTestApp/App/WasmBasicTestApp.csproj	Added WasmFilesToIncludeInFileSystem declarations for testing
src/mono/wasm/testassets/WasmBasicTestApp/App/FilesToIncludeInFileSystemTest.cs	Test code to verify VFS file existence
src/mono/wasm/testassets/JavascriptBundlers/rollup.config.mjs	Updated rollup to handle .txt files
src/mono/wasm/Wasm.Build.Tests/FilesToIncludeInFileSystemTests.cs	Integration test for VFS functionality
src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets	MSBuild integration for WasmFilesToIncludeInFileSystem
eng/testing/scenarios/BuildWasmAppsJobsList.txt	Registered new test class for CI

[maraf]

/ba-g Failure is unrelated timeout