Refactor MediaProjection stop-on-lock

Encapsulate all the MediaProjection stop behavior in a new stop
controller. This helps add more tests and keeping the callbacks more
isolated to help clean up MediaProjectionManagerService.

Bug: 377877538
Test: atest MediaProjectionStopControllerTest
Flag: EXEMPT refactor
Change-Id: I0667776e6fa58830dd6ef278c586c7f3b06dfe88