Add refract intrinsic

See: https://github.com/gpuweb/gpuweb/pull/1901

Bug: tint:950
Change-Id: I6f00ab753a2ddf2374352ddf636e1abfebe86ba7
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/56777
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>

src/sem/intrinsic_type.cc

@@ -193,6 +193,9 @@ IntrinsicType ParseIntrinsicType(const std::string& name) {
   if (name == "reflect") {
     return IntrinsicType::kReflect;
   }
+  if (name == "refract") {
+    return IntrinsicType::kRefract;
+  }
   if (name == "reverseBits") {
     return IntrinsicType::kReverseBits;
   }
@@ -436,6 +439,8 @@ const char* str(IntrinsicType i) {
       return "pow";
     case IntrinsicType::kReflect:
       return "reflect";
+    case IntrinsicType::kRefract:
+      return "refract";
     case IntrinsicType::kReverseBits:
       return "reverseBits";
     case IntrinsicType::kRound:

src/sem/intrinsic_type.h

@@ -88,6 +88,7 @@ enum class IntrinsicType {
   kPack4x8unorm,
   kPow,
   kReflect,
+  kRefract,
   kReverseBits,
   kRound,
   kSelect,