Merge changes from topic "sysprop"

* changes:
  BUILD_BROKEN_DUP_SYSPROP as escape hatch for the new sysprop restriction
  pm.dexopt.* props in runtime_libart.mk becomes optional
  Some properties are set as optional
  ro.zygote in base_system.mk is optional
  Don't inherit tablet-dalvik-heap for GSI and emulator
  Support optional prop assignments