[RESTRICT AUTOMERGE] Ignore small source rect hint

Which may be abused by malicious app to create a non-visible PiP
window that bypasses the background restriction.

Bug: 270368476
Test: Manually, using the POC app
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:4fda9095ba9bdecb8250336d4f0ca328ed7c2aea)
Merged-In: I3531a64fc67a1b6c43997ee33b7a7d4ab4e2d985
Change-Id: I3531a64fc67a1b6c43997ee33b7a7d4ab4e2d985