Tooltip: Add tooltip content to an aria-live div when the tooltip conten...

...t changes to allow support for all ATs. Fixes #9610. Tooltip announcements don't work in all browsers and AT combinations.

New and improved version now with:
1) no change to core, and
2) works across documents (theoretically because the focus events don't fire so you have to mouseover to get the tooltips to appear for the small number of elements where this still works)