Separated the Vulkan Validation Layers, Loader, Tools and Headers into
separate dirs to map to the new separate repo structure.

Bug: angleproject:2558
Change-Id: I422038f7dd7efe8c5b7a49dc5074de5caf40edfa
Reviewed-on: https://chromium-review.googlesource.com/1071880
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>