Adds aria tree rtl active descendant example to dev-app

[essjay05]

Creates tree-rtl-active-descendant-example files and adds it to the dev-app to be available for A11y testing.

[github-actions[bot]]

Deployed dev-app for 60872fbbc24d1b4da0096c3b8876ee1096e4810c to: https://ng-dev-previews-comp--pr-angular-components-32191-dev-wprppo0t.web.app

Note: As new commits are pushed to this pull request, this link is updated after the preview is rebuilt.

[wagnermaciel]

It looks like checkmark positioning is broken in the RTL example. Also, I think it makes sense to solely showcase the RTL aspect instead of RTL + active descendant