Add CommittedPrimitiveIndex test on a multi-triangle BLAS

Introduces a 3-triangle BLAS (tiled along x at x = -4, 0, +4) and a
3-lane dispatch that fires one ray per lane straight down at its own
triangle. Each lane's CommittedPrimitiveIndex() must equal its lane
index. Also exercises divergent rays per thread.

Part of the inline-RT test coverage epic
(#1258).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: MarijnS95

test/Feature/InlineRT/primitive-index.test

@@ -0,0 +1,85 @@
+#--- source.hlsl
+
+[[vk::binding(0, 0)]] RaytracingAccelerationStructure Scene : register(t0);
+[[vk::binding(1, 0)]] RWStructuredBuffer<uint> Output : register(u0);
+
+[numthreads(3,1,1)]
+void main(uint3 tid : SV_DispatchThreadID) {
+  // Three triangles tiled along x at x = -4, 0, 4. Each lane fires a ray
+  // straight down at its own triangle, so CommittedPrimitiveIndex() must
+  // be exactly the lane index. Also exercises divergent rays per thread.
+  RayDesc Ray;
+  Ray.Origin = float3((float(tid.x) - 1.0) * 4.0, 0, 1);
+  Ray.Direction = float3(0, 0, -1);
+  Ray.TMin = 0.0;
+  Ray.TMax = 100.0;
+  RayQuery<RAY_FLAG_NONE> Q;
+  Q.TraceRayInline(Scene, RAY_FLAG_NONE, 0xFF, Ray);
+  Q.Proceed();
+  Output[tid.x] = Q.CommittedStatus() == COMMITTED_TRIANGLE_HIT
+                      ? Q.CommittedPrimitiveIndex()
+                      : 0xFFFFFFFF;
+}
+//--- pipeline.yaml
+---
+Shaders:
+  - Stage: Compute
+    Entry: main
+Buffers:
+  - Name: Vertices
+    Format: Float32
+    Stride: 12
+    # Three triangles, one per lane, centered at x = -4, 0, +4.
+    Data: [ -4.0,  1.0, 0.0, -5.0, -1.0, 0.0, -3.0, -1.0, 0.0,
+             0.0,  1.0, 0.0, -1.0, -1.0, 0.0,  1.0, -1.0, 0.0,
+             4.0,  1.0, 0.0,  3.0, -1.0, 0.0,  5.0, -1.0, 0.0 ]
+  - Name: Output
+    Format: UInt32
+    Stride: 4
+    FillSize: 12
+  - Name: Expected
+    Format: UInt32
+    Stride: 4
+    Data: [ 0, 1, 2 ]
+AccelerationStructures:
+  BLAS:
+    - Name: MultiTriangleBLAS
+      Triangles:
+        - VertexBuffer: Vertices
+          VertexFormat: RGB32Float
+          VertexStride: 12
+          VertexCount: 9
+  TLAS:
+    - Name: Scene
+      Instances:
+        - BLAS: MultiTriangleBLAS
+DescriptorSets:
+  - Resources:
+    - Name: Scene
+      Kind: AccelerationStructure
+      DirectXBinding:
+        Register: 0
+        Space: 0
+      VulkanBinding:
+        Binding: 0
+    - Name: Output
+      Kind: RWStructuredBuffer
+      DirectXBinding:
+        Register: 0
+        Space: 0
+      VulkanBinding:
+        Binding: 1
+Results:
+  - Result: PrimitiveIndex
+    Rule: BufferExact
+    Actual: Output
+    Expected: Expected
+...
+#--- end
+
+# REQUIRES: acceleration-structure
+# XFAIL: Clang
+
+# RUN: split-file %s %t
+# RUN: %dxc_target -T cs_6_5 -Fo %t.o %t/source.hlsl
+# RUN: %offloader %t/pipeline.yaml %t.o