Expose OverlayProperties class and some APIs.

 - Expose Display#getOverlaySupport
 - Expose OverlayProperties#supportMixedColorSpaces
 - For virtual displays, we provide a default overlay properties with
   RGBA8888, SRGB and true for mixed color spaces support because it's
   always GPU.
 - Add @FlaggedApi for trunk stable release

Bug: 267234573
Test: builds
Change-Id: If2701d536cd1e2ff5d0d95993a3d2b00bff541c5