Moves the various broadcast receivers out of GlobalScreenshot and
adds unit tests for them, along with some other changes to make
them more easily testable:
- ScreenshotSmartActions is now a stateless injectable class,
instead of a collection of static methods
- DeleteImageInBackgroundTask removed, in favor of just calling
a background executor directly
- remove the TargetChosenReceiver (used to remove notifications
after a share target is chosen) since we're not using
notifications anymore
Bug: 160325487
Test: atest SystemUITests, plus manually checked that screenshots
continue to function as expected
Change-Id: I1c054dddd76404f385e59f7ab7317beaafde1106
c07f0a910f