fix: tree selection default behavior + warning, and updating other examples with incorrect a11y info

[smhigley]

This fixes a few issues with Tree that stem from having multiple actions on the same leaf node:

• For selection, this is impossible to fully avoid, but now by default the click action on the treeitem toggles selection if an author has not passed in an onClick handler. This allows selection to work with voice control, mobile screen readers, and macOS VoiceOver (or at least as long as the external team doesn't explicitly make it inaccessible).
• This PR removes the Customizing Interaction example, which demonstrates a pattern that is widely inaccessible. We need to tell consumers that they cannot define multiple interactions per leaf node -- or at least if they do, they're intentionally ignoring our advice and will end up with an inaccessible experience that we do not support.
• Adds more explicit docs wording around the accessibility pitfalls of trees.

Fixes ADO issue

[github-actions]

📊 Bundle size report

Package & Exports	Baseline (minified/GZIP)	PR	Change
react-components react-components: entire library	1.293 MB 325.786 kB	1.293 MB 325.815 kB	108 B 29 B
react-tree FlatTree	135.571 kB 40.413 kB	135.679 kB 40.443 kB	108 B 30 B
react-tree PersonaFlatTree	137.417 kB 40.931 kB	137.525 kB 40.956 kB	108 B 25 B
react-tree PersonaTree	133.498 kB 39.718 kB	133.606 kB 39.747 kB	108 B 29 B
react-tree Tree	131.658 kB 39.221 kB	131.766 kB 39.252 kB	108 B 31 B

Unchanged fixtures

Package & Exports	Size (minified/GZIP)
react-components react-components: Button, FluentProvider & webLightTheme	66.281 kB 19.002 kB
react-components react-components: Accordion, Button, FluentProvider, Image, Menu, Popover	225.836 kB 67.998 kB
react-components react-components: FluentProvider & webLightTheme	39.504 kB 13.112 kB
react-portal-compat PortalCompatProvider	5.341 kB 2.146 kB
react-timepicker-compat TimePicker	140.677 kB 45.99 kB

_{🤖 This report was generated against 838a28171bc01fdaf6139104225f35e6b7621e09}

[github-actions]

Pull request demo site: URL

[github-actions]

🕵🏾‍♀️ visual changes to review in the Visual Change Report

vr-tests-react-components/Menu 1 screenshots

Image Name	Diff(in Pixels)	Image Type
vr-tests-react-components/Menu.Nested Submenus Small Viewport Stacked.nested menu.chromium.png	856	Changed

vr-tests-react-components/Menu Converged - submenuIndicator slotted content 2 screenshots

Image Name	Diff(in Pixels)	Image Type
vr-tests-react-components/Menu Converged - submenuIndicator slotted content.default.submenus open.chromium.png	413	Changed
vr-tests-react-components/Menu Converged - submenuIndicator slotted content.default - RTL.submenus open.chromium.png	404	Changed

vr-tests-react-components/Positioning 2 screenshots

Image Name	Diff(in Pixels)	Image Type
vr-tests-react-components/Positioning.Positioning end.updated 2 times.chromium.png	65	Changed
vr-tests-react-components/Positioning.Positioning end.chromium.png	17	Changed

vr-tests-react-components/ProgressBar converged 1 screenshots

Image Name	Diff(in Pixels)	Image Type
vr-tests-react-components/ProgressBar converged.Indeterminate + thickness - High Contrast.default.chromium.png	84	Changed

vr-tests-react-components/Skeleton converged 1 screenshots

Image Name	Diff(in Pixels)	Image Type
vr-tests-react-components/Skeleton converged.Translucent Skeleton with rectangle.default.chromium.png	12	Changed

vr-tests-react-components/Tree 5 screenshots

Image Name	Diff(in Pixels)	Image Type
vr-tests-react-components/Tree.flat tree multi selection - Dark Mode.flat tree multi selection selected 1-1.chromium.png	97	Changed
vr-tests-react-components/Tree.flat tree multi selection - High Contrast.flat tree multi selection selected 1-1.chromium.png	87	Changed
vr-tests-react-components/Tree.flat tree multi selection.flat tree multi selection selected 1-1.chromium.png	151	Changed
vr-tests-react-components/Tree.flat tree single selection - High Contrast.flat tree single selection selected 1.chromium.png	13	Changed
vr-tests-react-components/Tree.flat tree single selection - RTL.flat tree single selection selected 1.chromium_2.png	48	Changed

There were 3 duplicate changes discarded. Check the build logs for more information.