Add flag for MediaRouter2-based InfoMediaManager

InfoMediaManager.createInstance() will gate MediaRouter2-based and
MediaRouter2Manager-based instances based on the new flag.

Also, return a NoOpInfoMediaManager when the target package name does
not exist.

Bug: 192657812
Test: Testmapping + Manual Flag Testing
Change-Id: I8dcdd1c1366ee4246b8a4805f2347a810f51afec