tint/intrinsics.def: Implement saturate()

Fixed: tint:1591
Change-Id: I0b1397d74abd49cd44caf326a2063e50c5cf07de
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/101480
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Auto-Submit: Ben Clayton <bclayton@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/tint/sem/builtin_type.cc

@@ -225,6 +225,9 @@ BuiltinType ParseBuiltinType(const std::string& name) {
     if (name == "round") {
         return BuiltinType::kRound;
     }
+    if (name == "saturate") {
+        return BuiltinType::kSaturate;
+    }
     if (name == "select") {
         return BuiltinType::kSelect;
     }
@@ -493,6 +496,8 @@ const char* str(BuiltinType i) {
             return "reverseBits";
         case BuiltinType::kRound:
             return "round";
+        case BuiltinType::kSaturate:
+            return "saturate";
         case BuiltinType::kSelect:
             return "select";
         case BuiltinType::kSign:

src/tint/sem/builtin_type.h

@@ -97,6 +97,7 @@ enum class BuiltinType {
     kRefract,
     kReverseBits,
     kRound,
+    kSaturate,
     kSelect,
     kSign,
     kSin,