Vulkan: Split tree ops into separate files.
This makes the design consistent. Added new files for
NameEmbeddedStructs and RewriteStructSamplers.
Bug: angleproject:2665
Bug: angleproject:2494
Change-Id: If7d22a6ce9a86d51d38f68787006b7a28957861e
Reviewed-on: https://chromium-review.googlesource.com/1108086
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
