Recycle ActivityStarter instances.

This changelist adds the ability to reuse ActivityStarter instances
by reclaiming spent ones. By default, ActivityStarters will now be
reset and be part of a pool for future activity start uses.

Bug: 64750076
Test: atest FrameworksServicesTests:StartActivityControllerTests
Test: atest FrameworksServicesTests:ActivityStarterTests

Change-Id: I77261ba6f397471f4aeb9ef6dfe5edcf55f0007f