Allow priviledged apps to do cross-package fully trusted embedding.

This change allows any package with the existing MANAGE_ACTIVITY_TASKS
signature permission to do cross-package trusted embedding.

Bug: 298025023
Test: verified locally that systemui can now embed home controls activity
Flag: NA
Change-Id: I3f7556c6dc4312ab5d40c3e3ddd9ea2f70413abf