Formalize overscan metrics.

The window manager now maintains and reports a new formal
"overscan insets" for each window, much like the existing
content and visible insets.  This is used to correctly
position the various UI elements in the various combination
of layout options.  In particular, this allows us to have
an activity that is using fitSystemWindows to have the content
of its UI extend out to the visible content part of the screen
while still positioning its fixed UI elements inside the
standard content rect (and the entire window extending all
the way into the overscan area to fill the screen as desired).

Okay, maybe that is not written so clearly.  Well, it made
my head hurt too, so suffer!

The key thing is that windows now need to know about three
rectangles: the overall rectangle of the window, the rectangle
inside of the overscan area, and the rectangle inside of the
content area.  The FLAG_LAYOUT_IN_OVERSCAN option controls
whether the second rectangle is pushed out to fill the entire
overscan area.

Also did some improvements to debug dumping in the window
manager.

Change-Id: Ib2368c4aff5709d00662c799507c37b6826929fd