Move gn setup for vulkan library/headers into their own third_party directory.

Bug: skia:
Change-Id: I4605f0d962271efb77bf3c17f1b0daaaddfb51c8
Reviewed-on: https://skia-review.googlesource.com/128540
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
3 files changed