Vulkan: Remove ShaderVariableType and flatten info map With the conversion of the interface variable info map keys to SPIR-V ids, there is no longer a benefit to bucket resources by their type. This change removes this bucketing and flattens the map. Bug: angleproject:7220 Change-Id: If83cb02ca9e91f72dddb2deb7313fee40f9f06c3 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4632577 Reviewed-by: Yuxin Hu <yuxinhu@google.com> Reviewed-by: Charlie Lao <cclao@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>