Vulkan: Add command buffer performance counter. Adds a counter for the secondary command buffers (non-RenderPass). We'll use this in an upcoming test that validates that ANGLE only issues a single barrier (CB) in some buffer read/write scenarios. Also adds a PerfCounters struct. Bug: angleproject:4429 Change-Id: Iaf75ca89da3d02753897cb4066e2c56db497417e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2334090 Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>