Implement the extension GL_AMD_gpu_shader_half_float_fetch

- Support new opaque types: f16sampler*, f16image*, f16subpassInput*.
- Add new built-in GLSL texture/image functions.

glslang/MachineIndependent/SymbolTable.cpp

@@ -75,6 +75,9 @@ void TType::buildMangledName(TString& mangledName) const
     case EbtAtomicUint:         mangledName += "au";     break;
     case EbtSampler:
         switch (sampler.type) {
+#ifdef AMD_EXTENSIONS
+        case EbtFloat16: mangledName += "f16"; break;
+#endif
         case EbtInt:   mangledName += "i"; break;
         case EbtUint:  mangledName += "u"; break;
         default: break; // some compilers want this