Canvas fontStretch should be renamed to fontWidth for CSS parity

[KurtCattiSchmidt]

What is the issue with the HTML Standard?

The CSSWG resolved to rename font-stretch to font-width last year: w3c/csswg-drafts#551 (comment)

Now that vendors are implementing this change, it was discovered that the corresponding Canvas API is now out-of-sync (see https://bugzilla.mozilla.org/show_bug.cgi?id=1911075).

For backwards compatibility, the CSSWG is keeping font-stretch as an alias for font-width, and it probably makes sense to do that here.

[annevk]

Not a big fan of adding aliases, but I guess it's okay.

cc @whatwg/canvas