[WGSL] Constant function for abs is wrong for u32 and f16

https://bugs.webkit.org/show_bug.cgi?id=265257
rdar://118724534

Reviewed by Mike Wyrzykowski.

For some reason it was casting u32 to int, when the result should be the identity.
The result type also needs to be explicit, otherwise we return f32 for f16 inputs.

* Source/WebGPU/WGSL/ConstantFunctions.h:
(WGSL::UNARY_OPERATION):

Canonical link: https://commits.webkit.org/271072@main

Source/WebGPU/WGSL/ConstantFunctions.h

@@ -783,9 +783,9 @@ CONSTANT_TRIGONOMETRIC(Cosh, cosh);
 CONSTANT_TRIGONOMETRIC(Sinh, sinh);
 CONSTANT_TRIGONOMETRIC(Tanh, tanh);
 
-UNARY_OPERATION(Abs, Number, [&](auto n) {
+UNARY_OPERATION(Abs, Number, [&]<typename T>(T n) -> T {
     if constexpr (std::is_same_v<decltype(n), uint32_t>)
-        return static_cast<uint32_t>(std::abs(static_cast<int32_t>(n)));
+        return n;
     else
         return std::abs(n);
 });