DisplayCutout: Draw anti-aliased bounds in soft overlay

To do so, we cannot use the Region from DisplayCutout, because it is conceptionally
a binary Bitmap. Instead, we need the exact curve as a Path.

Also fixes a theoretical bug where the DisplayCutout
was cached even though the display height changed.

Change-Id: I9356f4589186fedc5dc95010c7bd1a1fa20edf5e
Fixes: 77868940
Test: Enable display cutout in developer options, verify the edges look smoth and not jagged.
Test: atest DisplayCutoutTest