Set sampler feedback shader flag when sampler feedback operations are used (and validator version >= 1.9)

[Icohedron]

Fixes #8533

This PR sets the sampler feedback DXIL feature flag in the presence of sampler feedback operations when the validator version is >= 1.9.
A lit test has also added to verify the functionality.

Assisted-by: Claude Opus 4.8

[Icohedron]

I could also add a validator test but I don't think it is necessary. The validator already has two smoke tests ensuring that the validator validates the setting of shader flags. Explicit support for new shader flags does not need to be added to the validator since they are picked up automatically from DxilShaderFlags.cpp.

diff --git a/tools/clang/unittests/HLSL/ValidationTest.cpp b/tools/clang/unittests/HLSL/ValidationTest.cpp
index 67c22e7b..f1fb6208 100644
--- a/tools/clang/unittests/HLSL/ValidationTest.cpp
+++ b/tools/clang/unittests/HLSL/ValidationTest.cpp
@@ -217,6 +217,7 @@ public:
 
   TEST_METHOD(WhenMetaFlagsUsageDeclThenOK)
   TEST_METHOD(WhenMetaFlagsUsageThenFail)
+  TEST_METHOD(WhenMetaFlagsSamplerFeedbackThenFail)
 
   TEST_METHOD(WhenRootSigMismatchThenFail)
   TEST_METHOD(WhenRootSigCompatThenSucceed)
@@ -1843,6 +1844,17 @@ TEST_F(ValidationTest, WhenMetaFlagsUsageThenFail) {
                           "Flags must match usage");
 }
 
+TEST_F(ValidationTest, WhenMetaFlagsSamplerFeedbackThenFail) {
+  if (m_ver.SkipDxilVersion(1, 9))
+    return;
+  RewriteAssemblyCheckMsg(
+      "FeedbackTexture2D<SAMPLER_FEEDBACK_MIN_MIP> fb; Texture2D<float> t; "
+      "SamplerState s; float main() : SV_Target { "
+      "fb.WriteSamplerFeedback(t, s, (float2)0); return 0; }",
+      "ps_6_5", "67108864", "0", // remove the sampler feedback flag
+      "Flags must match usage");
+}
+
 TEST_F(ValidationTest, StorePatchControlNotInPatchConstantFunction) {
   if (m_ver.SkipDxilVersion(1, 3))
     return;

[hekota]

LGTM!