Add an public api to create a DisplayCutout with path for test only

Currently, there is no way to construct a DisplayCutout with cutout
path.
Androidx and camera app need an way to create a DisplayCutout with path
data for testing and they can only access public API. For test purpose,
we add a public API for it.

Bug: 212191782
Test: atest DisplayCutoutTests
Change-Id: I3118b01447cb77df6245f76c9abcb01ef69e80ec