Add configuration for maximum UI width.

This changelist adds config_maxUiWidth, a new system resource
configuration which specifies the maximum width the user interface
can operate in. If the physical or specified width is greater than
this value, dimensions and density are scaled down accordingly. The
native mode resolution can be still discovered through
Display.Mode#getPhysicalWidth/getPhysicalHeight.

Test: Defined override for development device and verified values.
Test: bit FrameworksServicesTests:com.android.server.wm.DisplayContentTests#testMaxUiWidth
Change-Id: I12e7ad52f2aa8014e143bc7e80b020c9b24ed9c8
Fixes: 25820708