Vulkan: Prep variable info map to remove hashing. The removes all the string-based query APIs from the program executable descriptor set init. The new APIs still use string-keyed maps but will be switched out with non-hashed maps in a future CL. Bug: angleproject:4524 Change-Id: I427efb3ebcf22d5fbdf6d20679bbdaa23cd2dc94 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3573077 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Yuxin Hu <yuxinhu@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>