Fix some issues in FrameworkInputMethodSystemServerTests

- Fix wrong src path in InputMethodSystemServerTests/Android.bp by CL[1]
- In IMMS, Make ImeTrackerService by CL[2] can inject a test looper, in
  case InputMethodManagerServiceTestBase#setUp got exception by null
  looper queue.
- Remove unused test method IMMS#getVisibilityStateComputer().
- Add ImfLock block in IMMS#getVisibilityApplier for fixing linter
  check.
- Fix a potential NPE when calling mImeTrackerService.onImmsUpdate that
  the statsToken may null during testing.
- Remove duplicate calls in testApplyImeVisibility_throwForInvalidState.
- Add missed showFlag parameters in testPerformShowIme.
- Fix verifyShowSoftInput logic when no need to verify showFlags cases
- Add a regression unit test In ImeVisibilityStateComputerTest for
  Bug 265439883:
  testComputeState_lastImeRequestedVisible_preserved_When_StateUnChanged

 [1]: I84f1a1b25eef4a757d8da27807285e08417458b4
 [2]: I432bab2de58a9df2c421bb00946ab211de445660

Bug: 246309664
Bug: 240359838
Test: atest FrameworkInputMethodSystemServerTests all passed
Change-Id: I0890641868f9200c613af0d6ee7014e4c7b1e7ed