angle_headers

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]>