[WGSL] quantizeToF16 generates invalid code for vectors

https://bugs.webkit.org/show_bug.cgi?id=267108
rdar://120500374

Reviewed by Mike Wyrzykowski.

The code generator was always emitting `float(half(x))` for quantizeToF16, but
it should to be `floatN(halfN(x))` if the argument is a vector of size N.

* Source/WebGPU/WGSL/Metal/MetalFunctionWriter.cpp:
(WGSL::Metal::emitQuantizeToF16):

Canonical link: https://commits.webkit.org/272685@main

Source/WebGPU/WGSL/Metal/MetalFunctionWriter.cpp

@@ -1716,8 +1716,12 @@ static void emitPack4xU8Clamp(FunctionDefinitionWriter* writer, AST::CallExpress
 
 static void emitQuantizeToF16(FunctionDefinitionWriter* writer, AST::CallExpression& call)
 {
-    writer->stringBuilder().append("float(half(");
-    writer->visit(call.arguments()[0]);
+    auto& argument = call.arguments()[0];
+    String suffix = ""_s;
+    if (auto* vectorType = std::get_if<Types::Vector>(argument.inferredType()))
+        suffix = String::number(vectorType->size);
+    writer->stringBuilder().append("float", suffix, "(half", suffix, "(");
+    writer->visit(argument);
     writer->stringBuilder().append("))");
 }