This roll moves Juggler component registration to a new system that
is used in XPCOM: this is what both RemoteAgent and Marionette use.
Drive-by: we now have to explicitly pass default values to dispatched
mouse events to avoid a `MOZ_ASSERT` trigger inside a drag service
native code.
Manual conflict resolutions: ab3ed0cb2c
Notable changes:
- javaScriptEnabled moved to the browser side.
- enabling new UI since it no longer helps to fix screencast
Review branch: https://github.com/aslushnikov/juggler/tree/roll-to-91-0-b10
Note: this will have 2 screencast tests failing. Investigation is in a follow-up.
