DO NOT MERGE: Allow corner UI to decouple from rounded_corner_radius

frameworks/base/core/res/res/dimens value rounded_corner_radius can
change not to reflect the actual device size due to tuning the rounding
on window corners.

This change allows us to decouple corner UI's idea of what the corner
size is from the framework dimension

Test: manual
Change-Id: I6548d74921d6e71250486984869572bdd304b0d0