Intent to prototype: screen.orientation.lock() is turned on Nightly

[Makoto Kato]

Hi.

screen.orientation.lock() is used on some sites such as YouTube to
lock the screen orientation to landscape/portrait. This API was turned
on Fennec (Former Firefox for Android). But when we moved to Fenix,
this became broken then disabled.

Cathy Lu (:calu) and I have re-implemented this API for
Fenix/GeckoView and Windows (tablet mode only due to Windows API
limitation), and fixed a lot of spec and compat issues. So I will turn
on this on Nightly for testing.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1767449
Standard: https://w3c.github.io/screen-orientation/
Standards Body: W3C
Preference: dom.screenorientation.allow-lock
DevTools: Devtools doesn't support screen orientation lock.
Platform coverage: Android / Windows (tablet mode only)
Other browsers: Supported in Blink (Android only) and WebKit Technical Preview
web-platform-tests: https://wpt.fyi/results/screen-orientation/

-- Makoto