Add BUILD_BROKEN_VENDOR_SEAPP_USES_COREDOMAIN

Starting from Android V, vendor seapp_contexts files can't assign
coredomain to vendor apps, as it's Treble violation. This build broken
variable is to suppress the enforcement for devices launching with U or
prior.

Bug: 280547417
Test: set BUILD_BROKEN_VENDOR_SEAPP_USES_COREDOMAIN := true and build
Change-Id: Ic4b5309f0d9bab9b93e88988d1a5a942b2de220a