WebGPU: Add command buffers and renderpass management Add a CommandBuffer class to serialize and replay WebGPU commands. Only Draw and SetPipeline are implemented in this patch. Manage render pass begin and end events due to framebuffer changes and swapping. Handle the color mask dirty bits so that a non-zero color mask will be used. All togther, this is enough to draw a triangle using a hard-coded shader without inputs. Bug: angleproject:0 Change-Id: I0fbf0296563c02c7f0774ad4197b83f4c93c22bb Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5731594 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Liza Burakova <liza@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>