Emit descriptor handle correctly for ParameterBlock<DescriptorHandle> (#8206)

In Metal, if `ParameterBlock` contains `DescriptorHandle` directly, it
would be emitted as DescriptorHandle literal, which is not valid Metal
code,

This fix adds a case for `kIROp_DescriptorHandleType` and directs it to
the Parent's `emitType` function to handle it.

1 files changed, 17 insertions, 0 deletions

diff --git a/tests/metal/test_descriptor_handle.slang b/tests/metal/test_descriptor_handle.slang
new file mode 100644
index 000000000..8579fee4a
--- /dev/null
+++ b/tests/metal/test_descriptor_handle.slang
@@ -0,0 +1,17 @@
+//TEST:SIMPLE(filecheck=CHECK): -stage compute -entry computeMain -target metal
+
+struct MyStruct
+{
+    uint value;
+}
+// CHECK-NOT: DescriptorHandle
+ParameterBlock<DescriptorHandle<Buffer<uint>>> param;
+RWStructuredBuffer<uint> outputBuffer;
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dtid : SV_DispatchThreadID)
+{
+    uint idx = dtid.x;
+    // Load values from the buffer to verify correct access
+    // CHECK: {{.*}}outputBuffer{{.*}}=
+    outputBuffer[idx] = param[0];
+}