Allow IME snapshot to capture with secure layer for transition

ImeContainer will set secure flag if the ime target is secured.
Allow to capture secure layer for IME snapshot when the snapshot is
used for transition, which shouldn't break b/215005011

Flag: EXEMPT bugfix
Bug: 351059374
Test: DisplayContentTests ZOrderingTests
Change-Id: Ib019bea1b1b1f6d8dbd3488e5e12d79503151b78