Vulkan: Move CommandBatch for threading support Will need access to CommandBatch class in threading worker. Bug: b/154030730 Change-Id: Ia79eab77a81b135c22bdeecbaf65bf3c301dc987 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2447442 Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Courtney Goeltzenleuchter <courtneygo@google.com>