Leverage WindowManagerInternal for private communication.

This CL changes following four methods from direct calling of
WindowManagerService to calling via WindowManagerInternal.
- getInputMethodWindowVisibleHeight
  (introduced by I0e920ee79c526c3aea6872b063cf294e2ab081c8)
- saveLastInputMethodWindowForTransition
  (introduced by Idf7700271cf882dfbf35c9d16f0f173a791221bc)
- isHardKeyboardAvailable
  (introduced by I8a6a4a7efce50bfaec114117e33f97f27b1ef950)
- setOnHardKeyboardStatusChangeListener
  (introduced by Ica768083f95c33dc1e494a28ba7d8b6eb989b0ef)

This CL does mechanical code moving and does not change any behaviors.

Bug: 22285167
Change-Id: I08e506050a0e495d62236b46e487848c967d185d