Add support for GL_NV_shader_sm_builtins

Including spirv and AST tests

Also increase size of TBuiltInVariable bitfields since we've now exceeded 127
and add a static_assert to make this easier to find next time it happens!

gtests/Spv.FromFile.cpp

@@ -410,6 +410,8 @@ INSTANTIATE_TEST_CASE_P(
         "spv.xfb2.vert",
         "spv.xfb3.vert",
         "spv.samplerlessTextureFunctions.frag",
+        "spv.smBuiltins.vert",
+        "spv.smBuiltins.frag",
     })),
     FileNameAsCustomTestSuffix
 );