RELAND of this commit. Had to fix fuzzer build errors.

Optimize performance of SecondaryCommandBuffers and enable them as the
default build option.
To disable this set angle_enable_custom_vulkan_cmd_buffers=false in
your build args.

This CL enhances the PoolAllocator to have a "fast" mode that can
be enabled at class creation. This mode uses an alignment of 1 byte and
enables a fastAllocation() call that avoids some bookkeeping overhead.
The SecondaryCommandBuffer uses this fastAllocation() function.
Furthermore the fast path of fast allocate, using the current page,
is inlined for maximum speed.
Jamie Madill also updated the SecondaryCommandBuffers to pre-allocate
blocks so that the commands occur linearly in memory. This speeds up
processing with improved cache coherency and minimizes overhead when
recording commands.
Also the core Draw functions and their state updates are all inlined
as well as the common functions to initialize commands and to copy
command pointer data.

This change also includes some new, custom commands. One is
imageBarrier that is a specialized version of pipelineBarrier that only
performs a single image layout transition.
There are customized versions of various Draw commands to minimize
copying of parameters.
There are also specialized commands to bind[Graphics|Compute]Pipeline
that have the pipeline type built in to the command.
More custom commands and command data size optimizations will be made
in follow-on commits.

Bug: angleproject:3136

Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1497418
Commit-Queue: Tobin Ehlis <tobine@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Change-Id: I621d8f8893308fca240b32390928e8ba0036cf06
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1535385Reviewed-by: Tobin Ehlis <tobine@google.com>