Allow mainline modules to set private window flags

We need to prevent apps from trying to decorate the permission grant
requests. Hence the the permission controller app (which will become a
mainline module) will need to set the
PRIVATE_FLAG_HIDE_NON_SYSTEM_OVERLAY_WINDOWS private window flag.

Test: Built
Bug: 110953302
Change-Id: I7dfed6aac8ec487ac0665ad33c2892cad416224a
3 files changed