Add a mechanism for accessible tooltips in core

[joedolson]

While we've worked hard to eliminate usage of the title attribute across most of WordPress core, there is still an occasional need for that type of contextual information, and the lack of it is a barrier to resolving some issues (e.g. #50921) and removing some of the last instances of the title attribute.

An accessible tooltip will need to meet these criteria:

1) Be available either via the mouse, via the keyboard, or via touch.
2) Be persistent until dismissed
3) Support primary & auxiliary usage, dependent on whether the tooltip is the sole name of the control or an elaboration of existing text.

Useful reference on accessible tooltips: ​https://inclusive-components.design/tooltips-toggletips/