Improve handling of built-in keyboard.

The window manager policy made some incorrect assumptions about the
meaning of the Configuration.keyboard field.  We need to be more
careful about distinguishing between built-in and external keyboards.

Most of this change is to move the determination of the parts of
the Configuration related to input devices into the WindowManagerService
leveraging new features of the InputManagerService to good effect.

Then we plumb through the flag that indicates whether a device
is internal or external so that we can be more particular about
how the lid switch effects changes to the Configuration.

Bug: 6424373
Change-Id: I36a1c22ade35e578955465a25940a33f227b9763