wgsl: Convert quantizeToF32 to used Math.fround (#3119)

Instead of passing the input through a F32Array, use the builtin
Math.fround.

This leads to a ~5% improvement benchmarking locally. This is less
than the equivalent f16 change, because F32Array is provided by the
runtime, whereas F16Array is being polyfilled, so is probably more
efficient to begin with.

src/webgpu/util/math.ts

@@ -2013,13 +2013,9 @@ export interface QuantizeFunc {
   (num: number): number;
 }
 
-/** Statically allocate working data, so it doesn't need per-call creation */
-const quantizeToF32Data = new Float32Array(new ArrayBuffer(4));
-
 /** @returns the closest 32-bit floating point value to the input */
 export function quantizeToF32(num: number): number {
-  quantizeToF32Data[0] = num;
-  return quantizeToF32Data[0];
+  return Math.fround(num);
 }
 
 /** @returns the closest 16-bit floating point value to the input */