Vulkan: Reserve enough storage for mSwapchainImages Investigation shows that when running traces in back to back mode, mSwapchainImages end up with max size of 6 or 7. This CL reserve the enough capacity (8 to be power of 2) so that no storage reallocation related data copy will occur. Similar storage is reserved for mSwapchainImageBindings as well. Bug: b/293297177 Change-Id: I1e216b6eaeed72554a20d27963b797b00ca5fd07 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6240592 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Charlie Lao <cclao@google.com>