Intent to prototype & ship: Canvas2d.fontKerning attribute

[Jonathan Kew]

Summary: In Firefox 104, I propose to implement & ship support for the
Canvas2d.fontKerning attribute.

This attribute gives authors control over font kerning in Canvas2d text,
just like the CSS font-kerning property does for HTML text.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1778908

Standard:
https://html.spec.whatwg.org/multipage/canvas.html#dom-context-2d-fontkerning

Platform coverage: All

Preference: None, this is a minor feature addition that I don't think
merits a pref.

DevTools bug: None required.

Other browsers: Shipping in Blink, although their implementation is a
bit buggy; filed
https://bugs.chromium.org/p/chromium/issues/detail?id=1343333 to get
this fixed. No signals from WebKit.

web-platform-tests: In /html/canvas/element/drawing-text-to-the-canvas
and /html/canvas/offscreen/text/