WM: Mark task overlays as trusted overlays

Seemingly every use of this going forward will also require
trusted overlay so it probably just makes sense to set it
in the infrastructure. We do some renaming and documentation
cleanup to make it a little more clear whats happening.

Bug: 213603716
Bug: 214239892
Test: Existing tests pass, manual.
Change-Id: Id55ef6bf439c6d911eb3f79cad7eaca2cc6cee17