Move tests to align with tested classes

A lot of tests remained in ActivityStarterTests that tested logic that
was moved out of ActivityStarter at some point (e.g into
BackgroundActivityStartController). This moved the BAL related tests
to BackgroundActivityStartControllerExemptionTests (other parts have
been moved to BackgroundActivityStartController*Tests before) and the
tests only test the actual BAL logic. Instead of testing
BackgroundLaunchProcessController related code in
BackgroundActivityStartController*Tests a new test class was created.

Flag: TEST_ONLY
Test: atest BackgroundActivityStartController*Tests ActivityStarterTests BackgroundLaunchProcessControllerTests
Bug: 345358113
Change-Id: I78cbca097278c172b854a80f899460537eb04e21