Intent to ship: screen.orientation.lock()

[Makoto Kato]

screen.orientation.lock() is used on some video sites such as YouTube to
lock the screen orientation to landscape/portrait. The past years, I
turned on it at Firefox Nightly by bug 1767449. I intend to enable
this methods on release channel.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1983483
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 (default is
off)
web-platform-tests: https://wpt.fyi/results/screen-orientation/