Intent to ship: transition-behavior property

[Boris Chiou]

As of fx129, I intend to turn `transition-behavior` CSS property on by default on all platforms. It has been developed behind the "layout.css.transition-behavior.enabled" preference.

Status in other browsers: Both Blink and WebKit have shipped this feature.

Bug to turn on by default: https://bugzilla.mozilla.org/show_bug.cgi?id=1901645

Standard: https://drafts.csswg.org/css-transitions-2/#transition-behavior-property

This feature was previously discussed in this "Intent to prototype" thread: https://groups.google.com/a/mozilla.org/g/dev-platform/c/jVSRE6JommI/m/fP4SBYt8BAAJ

Thanks.

Regards,

Boris