Allow holders of MANAGE_ACTIVITY_STACKS to launch on private displays

MANAGE_ACTIVITY_STACKS permission allows moving stacks, tasks and
activities between corresponding parents. It makes no sense to
require more strict START_ANY_ACTIVITY permission to launch on
private display, as an activity still can be moved to it.

Bug: 34164473
Test: 'adb unroot' and run android.server.cts.ActivityManagerDisplayTests
Change-Id: I3b59127829c432e42a46630025eeddd152bce1b0