CommandBuffer skeleton

CommandBuffer skeleton

The CommandBuffer object is a large portion of the Vulkan API.
To make reviewing it's implementation easier, this cl simply adds
all the CommandBuffer function signatures and UNIMLPEMENTED functions.

Bug b/116336664

Change-Id: I25ad8e6b15f46f9c18717f6f147d7d794eb1da97
Reviewed-on: https://swiftshader-review.googlesource.com/c/21608
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>