Let IME receive insets ignoring z-order

When IME is targeting notification shade, IME will be above status bar,
and IME won't receive status bar insets anymore. The surface position of
the control of IME will be changed because IME fits status bar. If the
IME control target receives the new IME control (new surface position)
after the IME animation starts, the IME position will be stale until the
next IME animation, because the controls would be copied before playing
the insets animation.

This CL lets IME receive insets no matter what z-order IME has. So the
IME position will stay the same while it is moved above system bars, and
the IME behavior will be the same as before Android S (receiving status
bar insets while targeting notification shade).

Fix: 186178729
Test: Steps as below:
1. Make, install, and open EditTextVariations.
2. Open menu, and select Direct Reply.
3. Expand notification shade.
4. Expand the notification of EditTextVariations.
5. Click Direct Teply Test.
6. See if IME is overlapped with (button-based) navigation bar.
   If no, press home button and repeat 3-6 for several times.
Change-Id: I53c64a5598f246ad577f652156903e4666a30cd9