Don't look through the buffer cache in protected contexts

Test: manual - protected content in Netflix apk, even without blurring

Without this change getOrCreateBackendTexture can return an
un-Protected backend texture when a Protected one is required.
This causes the Protected content draw to be dropped.

Note: This CL originally landed in main as part of a broader fix for
blurring protected content, but it has been discovered to fix other
issues with protected content that were otherwise still visible in
this branch.

Bug: 242266174
Bug: 294357792
Change-Id: I9d7bab890ae8d88656e77dede962b40e926580c8
(cherry picked from commit 59f71734)
Merged-In: I9d7bab890ae8d88656e77dede962b40e926580c8