Summary:
Since extensions does not have access to sharedApplication, give them an option to set the presentedViewController.
This will allow modules such as RCTAlertsManager to function correctly in extensions.
Changelog: [General] [Added] - Added RCTUtilsUIOverride as a way to shortcut obtaining presentedViewController from sharedApplication to a supplied view controller for extensions.
Reviewed By: PeteTheHeat
Differential Revision: D18620886
fbshipit-source-id: c752a6e328588f388e23be5270bf7da277182cca
Chunlok Lo