Test new tree in custom tree view

[alexr00]

Test for #63566

• Mac @joaomoreno
• Linux @octref
• Windows @lramos15

Complexity: 4

The goal of this test is compare the old tree based custom tree view to the new tree based custom tree view and check for differences. If you have an extension that you use that uses tree views, please try stable side by side with the pre-release build and make sure that in both the tree view works the same way(gitlens is a good option). Things to test:

• Expanded state preserves across reloads
• Alignment when there are icons next to twisties is good.
• Alignment when there are icons, but no icons next to twisties, is good
• Alignment when there are no icons is good
• Annotations, such as the source control annotations on files, in a custom view work, especially when resizing.
• Keyboard navigation still works
• Commands on expandable items
• Commands on non-expandable items
• Refreshing nodes
• Resizing behaves well
• Tree nodes can have an initial expanded state. Test that this works now.

If the extension you're testing with doesn't do all of these things, you can test with the tree view extension sample and modify it: https://github.com/microsoft/vscode-extension-samples/tree/master/tree-view-sample