Vulkan: Flatten shader interface variable maps This change removes duplicate entries added in the shader shader interface variable maps. One level of arrayness (indexed by shader type) is removed from these maps as now there is only a single entry per linked resource/etc. Bug: angleproject:7220 Change-Id: Ibf2d06a0e1f68e68797c2066f36e14cb9e667f77 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4628677 Reviewed-by: Yuxin Hu <yuxinhu@google.com> Reviewed-by: Charlie Lao <cclao@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>