[Material][Popover] Add support for virtual element as anchorEl

[DiegoAndai]

• I have followed (at least) the PR section of the contributing guide.

Changes

Add documentation, demo, and tests for using a virtual element (VE) as an anchor element for the Popover component.

• This doesn't require changes in the component, only to update the type and proptype for the anchorEl prop. Fixed previous definition: when providing a function for the anchor, the function doesn't receive any arguments.
• The virtual element is different from the one used for Popper and Tooltip, as the Popover expects the VE's nodeType property to be 1 (which is the type for Node.ELEMENT_NODE).

Screenshot of the new VE section on the docs

Closes #36416

[mui-bot]

Netlify deploy preview

• docs/data/material/components/popover/popover.md

Bundle size report

No bundle size changes

Generated by 🚫 dangerJS against 25c8838

[hbjORbj]

Can you explain this conditional: selection.anchorOffset === selection.focusOffset?

[DiegoAndai]

It checks that the selection doesn't start and ends at the same character. I tested that you could get that by creating the range programmatically, I don't know if you can get it just by interacting with it. In other words is to make sure that the selection spans at least one character.

[hbjORbj]

LGTM!