Consolidate ImeAwareEditText#scheduleShowSoftInput (1/2)

As InputMethodManager#isActive(View) may not always predictable as
reality since the method only check if the given view has been aligned
with the current served view, but not consider if the view has an active
input connection.

Test flakiness may happen when verifying showSoftInput should be invoked
after onStartInput but the event stream shows the reversed sequence.

Consolidate scheduleShowSoftInput by checking
IMM#hasActiveInputConnection to make sure showSoftInput request should
invoked after the input connection activated by the given focus view.

Bug: 176697749
Test: atest --iterations 100 KeyboardVisibilityControlTest#\
      testImeInvisibleWhenForceStopPkgProcess_Full
Change-Id: I466a93e2b4706ae809ac50dc16dc8e4ffa7c2f1c