Expand upon existing `ImageSubscript` support (Metal, GLSL, SPIRV) (#4408)

* Add additional `ImageSubscript` features:

1. Added ImageSubscript support for Metal & a test case
    * Merge GLSL/SPIRV/Metal `ImageSubscript` legalization pass
2. Added multisample support to glsl/spirv/metal for when using ImageSubscript
    * Added in this PR since the overhaul of the code merges together GLSL/SPIRV/Metal implementation
3. Fixed minor metal texture `Load`/`Read` bugs
    * [HLSL methods of access do not support subscript accessor for texture cube array](https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/texturecubearray)
    * removed swizzling of uint/int/float
    * other odd bugs which were causing compile errors

note: Compute tests do not work due to what seems to be the GFX backend (causes crash without error report). The tests are disabled.

* disable LOD with texture 1d

seems that LOD for 1d textures need to be a compile time constant as per an error metal throws

* syntax error in hlsl.meta

* static_assert alone with intrinsic_asm error

provides cleaner errors
Note: `static_assert` seems to be unstable and not be fully respected (still require `intrinsic_asm` to avoid a stdlib compile error)

* change comment to `// lod is not supported for 1D texture

* add `static_assert` in related code gen paths

* address review

* address review

* add asserts as per review comment, NOTE: unclear if these should be release 'asserts' as well

1 files changed, 41 insertions, 0 deletions

diff --git a/source/slang/slang-emit-metal.cpp b/source/slang/slang-emit-metal.cpp
index d38c3de9b..e7df29e0c 100644
--- a/source/slang/slang-emit-metal.cpp
+++ b/source/slang/slang-emit-metal.cpp
@@ -451,6 +451,47 @@ bool MetalSourceEmitter::tryEmitInstExprImpl(IRInst* inst, const EmitOpInfo& inO
             emitOperand(inst->getOperand(2), getInfo(EmitOp::General));
             return true;
         }
+        case kIROp_ImageLoad:
+        {
+            auto imageOp = as<IRImageLoad>(inst);
+            emitOperand(imageOp->getImage(), getInfo(EmitOp::General));
+            m_writer->emit(".read(");
+            emitOperand(imageOp->getCoord(), getInfo(EmitOp::General));
+            if(imageOp->hasAuxCoord1())
+            {
+                m_writer->emit(",");
+                emitOperand(imageOp->getAuxCoord1(), getInfo(EmitOp::General));
+            }
+            if(imageOp->hasAuxCoord2())
+            {
+                m_writer->emit(",");
+                emitOperand(imageOp->getAuxCoord2(), getInfo(EmitOp::General));
+            }
+            m_writer->emit(")");
+            return true;
+        }
+        case kIROp_ImageStore:
+        {
+            
+            auto imageOp = as<IRImageStore>(inst);
+            emitOperand(imageOp->getImage(), getInfo(EmitOp::General));
+            m_writer->emit(".write(");
+            emitOperand(imageOp->getValue(), getInfo(EmitOp::General));
+            m_writer->emit(",");
+            emitOperand(imageOp->getCoord(), getInfo(EmitOp::General));
+            if(imageOp->hasAuxCoord1())
+            {
+                m_writer->emit(",");
+                emitOperand(imageOp->getAuxCoord1(), getInfo(EmitOp::General));
+            }
+            if(imageOp->hasAuxCoord2())
+            {
+                m_writer->emit(",");
+                emitOperand(imageOp->getAuxCoord2(), getInfo(EmitOp::General));
+            }
+            m_writer->emit(")");
+            return true;
+        }
         default: break;
     }
     // Not handled