Add test to closesthit shader

Add test to closesthit.slang to test the slang
stdlib API: HitTriangleVertexPosition.

The new test will add the checking for extension declaration,
built-in declaration, and built-in variable access.

tests/vkray/closesthit.slang

@@ -1,5 +1,5 @@
 // closesthit.slang
-//TEST:SIMPLE(filecheck=CHECK): -profile glsl_460+GL_NV_ray_tracing -stage closesthit -entry main -target spirv-assembly
+//TEST:SIMPLE(filecheck=CHECK): -profile glsl_460+GL_EXT_ray_tracing -stage closesthit -entry main -target spirv-assembly
 //TEST:SIMPLE(filecheck=CHECK): -stage closesthit -entry main -target spirv-assembly -emit-spirv-directly
 
 struct ReflectionRay
@@ -30,19 +30,33 @@ void main(
 	color *= RayTCurrent() - RayTMin();
 
 	ioPayload.color = color;
+
+	uint index = 0U;
+	HitTriangleVertexPosition(index);
+
+	index = 1U;
+	HitTriangleVertexPosition(index);
+
+	index = 2U;
+	HitTriangleVertexPosition(index);
 }
 
 // CHECK: OpCapability RayTracing
+// CHECK: OpCapability RayTracingPositionFetchKHR
 // CHECK: OpEntryPoint ClosestHitNV %main "main"
 // CHECK-DAG: OpDecorate %[[INSTANCE_ID:[A-Za-z0-9_]+]] BuiltIn InstanceId
 // CHECK-DAG: OpDecorate %[[INSTANCE_INDEX:[A-Za-z0-9_]+]] BuiltIn InstanceCustomIndexNV
 // CHECK-DAG: OpDecorate %{{.*}} BuiltIn PrimitiveId
 // CHECK-DAG: OpDecorate %{{.*}} BuiltIn HitKindNV
 // CHECK-DAG: OpDecorate %{{.*}} BuiltIn RayTmaxNV
 // CHECK-DAG: OpDecorate %{{.*}} BuiltIn RayTminNV
+// CHECK-DAG: OpDecorate %{{.*}} BuiltIn HitTriangleVertexPositionsKHR
 // CHECK-DAG: %ShaderRecord{{.*}} = OpVariable %_ptr_ShaderRecordBufferNV{{.*}} ShaderRecordBufferNV
 // CHECK-DAG: %{{.*}} = OpVariable %_ptr_IncomingRayPayloadNV_ReflectionRay{{.*}} IncomingRayPayloadNV
 // CHECK-DAG: %{{.*}} = OpLoad %{{u?}}int %[[INSTANCE_ID]]
 // CHECK-DAG: %{{.*}} = OpLoad %{{u?}}int %[[INSTANCE_INDEX]]
 // CHECK-DAG: %{{.*}} = OpAccessChain %_ptr_ShaderRecordBufferNV_uint %ShaderRecord{{.*}} %int_0
 // CHECK-DAG: %{{.*}} = OpAccessChain %_ptr_IncomingRayPayloadNV_v4float %{{.*}} %int_0
+// CHECK-DAG: %{{.*}} = OpAccessChain %_ptr_Input_v3float %{{.*}} %{{u?}}int_0
+// CHECK-DAG: %{{.*}} = OpAccessChain %_ptr_Input_v3float %{{.*}} %{{u?}}int_1
+// CHECK-DAG: %{{.*}} = OpAccessChain %_ptr_Input_v3float %{{.*}} %{{u?}}int_2