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: If4035e6cbd0c62a1111241d94ed0a3923f61247b