feat(hover-service) make hover-service use platform showPopover()

[Alexander-Taran]

What it does

Prevents any z-index problems for hovers/

It makes HoverService use web platform [popover='hint'].
Which it turn puts them on "top-layer"
Popover API is baseline available now and some of us use it.
https://developer.mozilla.org/en-US/docs/Web/API/Popover_API

HoverService popovers had no chance of being on top of "true" popovers.
This PR addresses just that.
Screenshot of browser-only example with this change in place:

Bonus: It also allows to close such popovers with "Escape"

How to test

HoverService popovers should be visible and on top of everything else.

Follow-ups

Someday when options for showPopover() will be baseline available it would be possible to position them declaratively to target. So code that calculates position could be thrown away.
It is available in chromium based browsers already.

Attribution

on behalf of web standards and performance

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