Adds a content-intent-launching-activity flag to WearableExtender

This adds a flag to WearableExtender (and Action.WearableExtender)
indicating that the attached ContentIntent will launch an activity
on Wear, which lets the platform know that it can (and should)
generate a sleek transition for the launching of said intent (as
opposed to the intent causing change in the background).

Bug:28019194
Change-Id: Id8b422ea52c5e941e38558aaf31ce2cf4bb7c6f3