Rounded corner: fix layer settings when inherited from parent settings

This fixes a bug where the radius inherited from parent settings
were not scaled correctly. Also adds a unit test to test this scaling
behavior in the future.

Bug: 388410825

Test: atest surfaceflinger_unittest; manual - open PiP capable apps

Flag: EXEMPT bugfix
Change-Id: Ib63e27a75d3facecef94d8723b6cbdbe0cae6c27