This changes the fixed array into a STL vector. Instead of storing
Descriptor Pools by value we now store them by pointer. This allows the
vector to resize without changing the address of the Descriptor Pool.

Also enables some more Vulkan perf tests that were crashing before.

Bug: angleproject:2938
Change-Id: I8a88d5315b941c4f54205a9957e2834fe02ada84
Reviewed-on: https://chromium-review.googlesource.com/c/1311395
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tobin Ehlis <tobine@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>