fix(material/tooltip): prevent tooltip from showing when hovering unrelated elements

[pandikapinata]

A trigger can have a popover-based overlay nested inside it (e.g. an open mat-select panel), and that overlay's full-viewport backdrop ends up as a DOM descendant of the trigger. mouseenter fires on an element and all of its ancestors, so hovering anywhere on the page while such a backdrop was present re-fired mouseenter on the trigger, showing the tooltip even though the pointer wasn't visually near it.

Guards the mouseenter handler by checking that a trusted pointer event is actually within the trigger's own bounds before showing the tooltip.
Synthetic events dispatched in tests aren't trusted, so existing test coverage is unaffected.

Fixes #32747

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[pandikapinata]

recheck

[crisbeto]

This isn't a good way to fix it, because it can end up ignoring events from nested elements that may be sticking out of the trigger (e.g. how we have the touch targets on buttons). It'll break a ton of tests internally and it seems like it's breaking some of the external ones as well.