Intent to prototype and ship: overflow-clip-margin: <visual-box> and allow replaced elements to overflow their content box

[Emilio Cobos Álvarez]

Hi,

In bug 1999100 I plan to (after the soft-freeze) land support for
overflow-clip-margin: <visual-box> and allow replaced elements to
overflow their content box.

Note that view transitions already can overflow their content box, this
patch just extends the same functionality to <canvas> / <img> / <video>.

Specification:
* https://drafts.csswg.org/css-overflow-4/#overflow-control
* https://github.com/whatwg/html/issues/11986
* https://github.com/w3c/csswg-drafts/issues/13185
Standards Body: CSSWG + WHATWG
Platform coverage: All
Preference: None (extension to existing property)
DevTools bug: N/A
Extensions bug: N/A
Link to standards position: No specific position for this extension
Other browsers:
* Blink: Shipping for quite a while, though overflow: clip is a bit
broken: https://issues.chromium.org/issues/465987920
* WebKit: Not supported, same bug for overflow: clip:
https://bugs.webkit.org/show_bug.cgi?id=303544

Let me know if there's any concern.

Thanks,

-- Emilio