Metal: misc fixes and enable more tests. (shader-slang#4374)

* Fix and enable tests for metal.

* Fix.

* Fix.

* Fix tests.

* Fix warnings.

* Fix.

---------

Co-authored-by: Yong He <yonghe@Yongs-Mac-mini.local>

Author: csyonghe

source/slang/hlsl.meta.slang

@@ -149,9 +149,11 @@ alias cpp_glsl_hlsl_spirv = cpp | glsl | hlsl | spirv;
 alias cpp_glsl_hlsl_metal_spirv = cpp | glsl | hlsl | metal | spirv;
 alias cpp_hlsl = cpp | hlsl;
 alias cuda_glsl_hlsl = cuda | glsl | hlsl;
+alias cuda_hlsl_metal_spirv = cuda | hlsl | metal | spirv;
 alias cuda_glsl_hlsl_spirv = cuda | glsl | hlsl | spirv;
 alias cuda_glsl_hlsl_metal_spirv = cuda | glsl | hlsl | metal | spirv;
 alias cuda_glsl_spirv = cuda | glsl | spirv;
+alias cuda_glsl_metal_spirv = cuda | glsl | metal | spirv;
 alias cuda_hlsl = cuda | hlsl;
 alias cuda_hlsl_spirv = cuda | hlsl | spirv;
 alias glsl_hlsl_spirv = glsl | hlsl | spirv;