Intent to ship: implicit pointer capture for touch

[Edgar Chen]

Summary: In Firefox 91, I intend to enable implicit pointer capture for touch by default on all platforms, it has been developed behind the `dom.w3c_pointer_events.implicit_capture` preference which has been enabled by default on early beta for a while.

Bug to turn on by default: https://bugzilla.mozilla.org/show_bug.cgi?id=1669729

Standard: https://w3c.github.io/pointerevents/#implicit-pointer-capture

Platform coverage: all

Preference: dom.w3c_pointer_events.implicit_capture

DevTools bug: N/A

Other browsers: Both WebKit and Blink ship this.

web-platform-tests: in https://github.com/web-platform-tests/wpt/tree/master/pointerevents [1]

[1] Gecko test driver doesn't support generating touch action so far, we wrap wpt touch tests into mochitests in https://searchfox.org/mozilla-central/source/dom/events/test/pointerevents

Please let me know if you have any concerns.

Thank you

--

Edgar Chen