Allow resource override for PiP size spec

Putting the default/min size percentage value into resources so they
could be overridden on device basis.

Add a second set of default/minimum size percentage if the Display is
near square. This is to make sure the default PiP window does not
overlap with the hinge as much as possible.

Screenshot: before https://screenshot.googleplex.com/8mk7KozJ9g9d56K.png
Screenshot: after https://screenshot.googleplex.com/Z9dfdGzdJqJuZ5E.png
Bug: 318602602
Test: atest WMShellUnitTests:PhoneSizeSpecSourceTest
Change-Id: I890857db0aa415b700bf0b81d0d0c37968322e03