Add the possibility to modify the View focus rect

This change makes it possible for a view to supply a different rectangle than
the drawing rect to be used by the FocusFinder when finding a new view to give
focus to. This is useful if e.g. the total view area is larger than the
interactive area of the view.

The default implementation of getFocusRect() will return  getDrawingRect().
The existing behaviour is only changed if getFocusRect() is overridden by a
subclass of android.view.View

Change-Id: I52dd95c6fa296b744e354217051dcec1bb3c8e92