Merge changes from topic "sthal-2.4"

* changes:
  Adopt "resourcesAvailable" naming instead of "tryAgain"
  Send a tryAgain() when no longer at model capacity
  Send a tryAgain() event when external capture ends
  Unregister capture state listener
  Thread-safety improvements
  Move concurrent capture enforcement to compat layer
  Test refactoring
  Refactor ExternalCaptureStateTracker
  Move max number of models enforcement to compat layer
  Extract HAL reboot out of middleware implementation
  Make sure no excessive methods are called
  Small syntactic cleanups
  Support preemptive model unloading
  Support load preemption in SoundTriggerMiddleware
  Add support for start/load "busy" error code
  Dependency injection of STHAL compatibility
  Run existing SoundTriggerMiddlewareImplTest tests on v2.4
  Some small fixes and cleanup in SoundTriggerMiddlewareImplTest
  Add support for STHAL 2.4 at lower layers of middleware