Vulkan: Update ContextVk command buffer access methods. Use the following names: - flushAndBeginRenderPass - endRenderPassAndGetCommandBuffer - flushAndGetPrimaryCommandBuffer This clarifies that a flush is part of the method. Bug: angleproject:4029 Change-Id: I6c870761339ea7aa39c83142200781ba39ad6a4b Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2068129 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com> Reviewed-by: Tim Van Patten <timvp@google.com>