Only allow system and same app to apply relinquishTaskIdentity

Any malicious application could hijack tasks by
android:relinquishTaskIdentity. This vulnerability can perform UI
spoofing or spy on user’s activities.

This CL limit the usage which only allow system and same app to apply
relinquishTaskIdentity.

Bug: 185810717
Test: atest IntentTests
      atest testActivityWithRelinquishTaskIdentity
      atest com.android.server.wm.TaskTests
Change-Id: I55fe8938cd9a0dd7c0268e1cfec89d4e95eee049