Add support for Vulkan raytraicng "shader record" (#735)

The syntax for this is a placeholder for now, since we will probably want to migrate to whatever gets decided on for dxc. To declare that some data should be part of the "shader record" use `layout(shaderRecordNV)` to mirror the GLSL raytracing extension:

```hlsl
layout(shaderRecordNV)
cbuffer MyShaderRecord
{
    float4 someColor;
    uint   someValue;
}
```

The intention (not enforced) is that an application would map `MyShaderRecord` to "root constants" in the "local root signature" when compiling for DXR, while the output code in GLSL will always map to the shader record in Vulkan raytracing:

```glsl
layout(shaderRecordNV)
buffer MyShaderRecord
{
    float4 someColor;
    uint   someValue;
};
```

This change does *not* support declaring a global value of `struct` type with `layout(shaderRecordNV)` (or a `ParameterBlock` with the modifiers, although that would be a nice-to-have feature) and it does *not* support having the contents of the shader record be mutable (even if GLSL/Vulkan allows it). Those can/should be added in future changes.

In terms of implementation, this closely mirrors the way that `layout(push_constant)` buffers were being handled, where the data inside the `ConstantBuffer<X>` (the value of type `X`) gets laid out using ordinary rules (and consuming ordinary `UNIFORM` storage, while the buffer itself is given a different layout resource to reflect that fact that it does not consume a VK `binding` any more, but a different conceptual resource.

Note: an alternative design here (that might actually be preferrable) would be to have both push-constant and shader-record buffers be handled as alternative aliases for `ConstantBuffer` (or maybe `ParameterBlock`) so that you have, e.g.:

```hlsl
PushConstantBuffer<X> myPushConstants;
ShaderRecord<Y> myShaderRecord;
```

This alternative design avoids API-specific decorations on the declarations, and reflects the intent of the programmer very directly, even when they are compiling for a target like D3D that doesn't reflect these choices at the IL level (it could still be exposed through the Slang reflection API).

1 files changed, 7 insertions, 0 deletions

diff --git a/source/slang/parameter-binding.cpp b/source/slang/parameter-binding.cpp
index 58891a956..622474116 100644
--- a/source/slang/parameter-binding.cpp
+++ b/source/slang/parameter-binding.cpp
@@ -1184,6 +1184,13 @@ getTypeLayoutForGlobalShaderParameter_HLSL(
     auto rules = layoutContext.getRulesFamily();
     auto type = varDecl->getType();
 
+    if( varDecl->HasModifier<ShaderRecordNVLayoutModifier>() && type->As<ConstantBufferType>() )
+    {
+        return CreateTypeLayout(
+            layoutContext.with(rules->getShaderRecordConstantBufferRules()),
+            type);
+    }
+
     // We want to check for a constant-buffer type with a `push_constant` layout
     // qualifier before we move on to anything else.
     if (varDecl->HasModifier<PushConstantAttribute>() && type->As<ConstantBufferType>())