Does this issue occur when all extensions are disabled?: No - issue with trees contributed by any extension

• VS Code Version: 1.75.0-insider
• OS Version: Darwin x64 22.2.0

Steps to Reproduce:

I edited the tree-view-sample extension to provide a minimal reproducible example https://github.com/alexweininger/vscode-extension-samples/tree/alex/focus-never-unset/tree-view-sample

1. Clone and run the edited tree-view-sample
2. Before selecting or focusing any tree items, click the "Test View: Change Title" button on the view title bar.

Observe that the focusedNode and selectedNode arguments are both undefined as expected.

3. Select or focus a tree item.
4. Click the "Test View: Change Title" button again.

focusedNode is set as expected

5. Press the Escape key, or unfocus the tree with your mouse by clicking outside. The UI shows no focused items.

6. Without selecting or focusing tree items, click the "Trest View: Change Title" button.

Expect: focusedNode argument should be undefined.

Actual: focusedNode is set to the last node that had focus in the tree.

It seems that the focused item is unable to be "reset", and only able to change to a different item. I don't think this is intended behavior, since the UI doesn't display any item as being focused. This creates confusion as commands may act differently depending on if focusedNode is defined.