Vulkan: Fix Vulkan secondary command buffers This change abstracts initialization, begin/end, reset and recycle of command buffers such that both Vulkan and ANGLE secondary command buffers are supported. Bug: angleproject:6100 Change-Id: I8c79764ac98b599fda08fe45cf8c4f0a6573f0f9 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2987873 Reviewed-by: Jamie Madill <[email protected]> Reviewed-by: Tim Van Patten <[email protected]> Commit-Queue: Shahbaz Youssefi <[email protected]>