Hide the software input based on its state.

This is a 2nd trial of I20ae2749a which is reverted due to a regression.
The goals of this CL are two:
- Split setImeWindowStatus method into two: keeping IMS status and
  updating system UI e.g. NavBar icon state.
- Hide software keyboard based on a realistic IMS status.

IMMS#mImeWindowVis has been used for two purpose, keeping IMS status and
updating the NavBar icons, e.g. keyboard icon.
However, to update NavBar icon, sometimes IMMS#mImeWindowVis value is
updated without any notification from IMS. As the result, the status
value becomes incosistent with the real IMS state.
This patch extracts NavBar update logic into separate method and keeps
IMMS#mImeWindowVis as notified status. Then, use it for hiding software
input correctly in IMMS#hideCurrentInputLocked.

This CL also removes refreshImeWindowVisibilityLocked method including
workaround for fixing Bug 11186297. That issue is no longer
reproducible with latest lock screen and almost no effect for existing
users and developers.  So simply remove them in this CL.

BUG: 21446788
BUG: 20764441
BUG: 18722991
Change-Id: I33dc6278fd892f26e56352722bf9449b8b102030