SurfaceFlinger Input: Shrink frame by surfaceInsets.

Probably best explained by the comment in InputWindow.h. We can't
use touchable region because we need to shift the coordinate space.
As a follow-up I'm going to look in to shifting the coordinate space
on the client but it was very non obvious where to do so.

Test: Manual
Bug: 80101428
Bug: 113136004
Bug: 111440400
Change-Id: Ibbaffa89a80f3a047c716265251f547631bdf802