Consolidate handling occluded initializing activity

Since task fragment is introduced, forAllOccludedActivities may
not work as expected because individual task fragment has its
own occluding relationship. Without correcting that, it may
remove active starting window.

Though the method can be fixed by iterating task fragment with
bounds check, it increases the complexity to maintain another
partial logic of EnsureActivitiesVisibleHelper.

So it may be more efficient and simpler by reusing the core of
visibility update to call cancelInitializing. And because the
visibility update is common to be called when resuming, it can
provide the same effect. In this way, the long loop executed
every time (cancelInitializingActivities) when resuming any
activity is also eliminated.

Also
- Remove mStartingWindowState because the nullity of mStartingData
  has already indicated that.
- Move transferSplashScreenIfNeeded to removeStartingWindow because
  when calling removeStartingWindowAnimation, it should do the
  removal directly.

Bug: 189385912
Bug: 194193397
Test: ActivityRecordTests#testTransferStartingWindowFromFinishingActivity
      RootTaskTests#testClearUnknownAppVisibilityBehindFullscreenActivity
Change-Id: I4621c2215807e713d9142acc7814786de50d88c4