Vulkan: Add storage buffer support The storage buffers are placed in the same descriptor set as uniform buffers. Some refactoring is done to reuse code that handles UBOs to handle SSBOs as well. A good number of tests still fail as they test SSBOs in conjunction with compute shaders. Bug: angleproject:3561 Change-Id: Ia33c1f68e6f6402c746f5919ede87b2c308cf81c Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1687126 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com>