Set text toasts as trusted overlays

So that touches can pass through them (check go/untrusted-touches) and
since those are rendered by System UI.

Test: atest WindowUntrustedTouchTest
Test: Display a text toast, click it, verify touch is not flagged.
Bug: 158002302
Change-Id: Ib75a9db5839fff031288b4b5855c49f997187cca