Currently hitting a crash on Apple so disabling FramebufferVk cache.

Bug: angleproject:4442
Change-Id: I3824252210aeeaf9919c8d17730395b394a50862
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2080661Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Commit-Queue: Tobin Ehlis <tobine@google.com>