Vulkan: Add dynamic index buffers to graph With DynamicBuffer outputting BufferHelper objects, these objects can participate in the command graph, i.e. record commands. This means they need appropriate dependencies in the graph as well as pipeline barriers. There are a few users of DynamicBuffer for which this change should be applied to. This change covers index buffers. This commit includes a fix to BufferHelper::copyFromBuffer for WaW hazards. It also includes a fix for a missing pipeline barrier after BufferVk::copyToBuffer. Bug: angleproject:2958 Change-Id: I3e61af56936580b2da20c28c45defece552d9a39 Reviewed-on: https://chromium-review.googlesource.com/c/1352732 Reviewed-by: Tobin Ehlis <tobine@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>