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, 16 insertions, 2 deletions

diff --git a/source/slang/slang-emit-spirv.cpp b/source/slang/slang-emit-spirv.cpp
index 3ee0d9241..51a71d65c 100644
--- a/source/slang/slang-emit-spirv.cpp
+++ b/source/slang/slang-emit-spirv.cpp
@@ -2989,12 +2989,26 @@ struct SPIRVEmitContext
 
     SpvInst* emitImageLoad(SpvInstParent* parent, IRImageLoad* load)
     {
-        return emitInst(parent, load, SpvOpImageRead, load->getDataType(), kResultID, load->getImage(), load->getCoord());
+        if (load->hasAuxCoord1())
+        {
+            return emitInst(parent, load, SpvOpImageRead, load->getDataType(), kResultID, load->getImage(), load->getCoord(), SpvImageOperandsSampleMask, load->getAuxCoord1());
+        }
+        else
+        {
+            return emitInst(parent, load, SpvOpImageRead, load->getDataType(), kResultID, load->getImage(), load->getCoord());
+        }
     }
 
     SpvInst* emitImageStore(SpvInstParent* parent, IRImageStore* store)
     {
-        return emitInst(parent, store, SpvOpImageWrite, store->getImage(), store->getCoord(), store->getValue());
+        if (store->hasAuxCoord1())
+        {
+            return emitInst(parent, store, SpvOpImageWrite, store->getImage(), store->getCoord(), store->getValue(), SpvImageOperandsSampleMask, store->getAuxCoord1());
+        }
+        else
+        {
+            return emitInst(parent, store, SpvOpImageWrite, store->getImage(), store->getCoord(), store->getValue());
+        }
     }
 
     SpvInst* emitImageSubscript(SpvInstParent* parent, IRImageSubscript* subscript)