Add transition between LongScreenshotActivity and editor

Turned off by default.

Add an ImageView for the shared element transition, position it based
upon the crop bounds.

Finish the activity if the activity stops and a transition has begun.

Bug: 183197895
Test: Visual observation of transition
Change-Id: I4286622c39f74ea2a0d6de71423fc58599e3d2db
2 files changed