Fix security bug for TaskFragment creation

1. Check Task#effectiveUid instead of rootActivity Uid for TF creation
2. Pass in the caller uid/pid for activity starter instead of using
   Binder.getCallingUid() after clearCallingIdentity()

Bug: 205996115
Test: atest WmTests:TaskFragmentOrganizerControllerTest
Change-Id: I1b1470a95d55820dd6d69658c570c3e5640ebe55
5 files changed