spirv-val: Initial SPV_EXT_mesh_shader builtins

[spencer-lunarg]

Adds the basic validation of storage class and type for the 4 new builtins fromSPV_EXT_mesh_shader

[s-perron]

The smoke test is failing because of this change. The three failing tests are:

[  FAILED  ] Glsl/CompileToSpirv14Test.FromFile/spv_ext_meshShaderBuiltins_mesh, where GetParam() = "spv.ext.meshShaderBuiltins.mesh"
[  FAILED  ] Glsl/CompileToSpirv14Test.FromFile/spv_ext_meshShaderRedeclBuiltins_mesh, where GetParam() = "spv.ext.meshShaderRedeclBuiltins.mesh"
[  FAILED  ] Glsl/CompileToSpirv14Test.FromFile/spv_460_subgroupEXT_mesh, where GetParam() = "spv.460.subgroupEXT.mesh"

@sjfricke I'll merge, but you will need to either fix glslang or fix the errors in spir-v with a separate PR. Whatever needs to be done.

[spencer-lunarg]

@s-perron sounds good, there are some other mesh shading related issues I need to get to as well which might be related

[greg-lunarg]

The prevailing opinion is that the Vulkan spec is in error and the glslang tests are correct. Therefore this PR is partially in error. Please see KhronosGroup/glslang#3044

[greg-lunarg]

@s-perron I think a revert makes the most sense at this time. Thanks!