Replace showSoftInput with ImeAwareEditText.scheduleShowSoftInput

Both View focus (which is triggered by View.requestFocus()) and IME focus
(which is internally handled inside InputMethodManager), are implemented
as delayed tasks on the UI thread. The goal here is to make sure that
InputMethodManager.showSoftInput() always gets called only after the target
EditText gained IME focus.
This requires some tricks, but is basically a solved problem with
ImeAwareEditText introduced by
I182b05d3ff59fb3b4732d60d0d5a464f0e0e0235. Here we can just reuse it.

Note that ConfirmLockPassword & ChooseLockPassword are the only ones
using ScrollToParentEditText. Latter doesn't call IMM.showSoftInput().

Fixes: 62542157
Test: Verified keyboard still shows-up on the ConfirmLock screen.

Change-Id: I892d639f3cc5d43db553b682d5278b8ce2fe72da