Updated support for drawing background drawable when resizing

Updated support for drawing background drawable when resizing

f3a62fbc58bbc7f081a53248cae48a8951294e8f added support for drawing
the background draweable when resizing an activity window.
However, after some additional discussion we decided that
R.styleable.Window_windowResizingBackground and
R.integer.config_windowResizingBackgroundColorARGB are not needed.
We use R.styleable.Window_windowBackground for the background
drawable and fallback to using R.styleable.Window_windowBackgroundFallback
which is now public if the first isn't set.

Bug: 24534744
Change-Id: Ia0507e25a1893ea941d259f1d4e88ce500dda154