Vulkan: Remove VK_DESCRIPTOR_POOL_CREATE_FREE_DESCRIPTOR_SET_BIT Some virtual machine drivers have performance cost with VK_DESCRIPTOR_POOL_CREATE_FREE_DESCRIPTOR_SET_BIT. This CL keeps the individually freed descriptorSet in the pool and try to reuse rather than free it. This CL also removes descriptorSetCount from some API since it always allocate one at a time. Bug: b/237848471 Change-Id: I029d651101fa1050770eba9e733a166e56a69684 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3749797 Commit-Queue: Charlie Lao <cclao@google.com> Reviewed-by: Ian Elliott <ianelliott@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>