[js/webgpu] Replace array with string in transpose perm (#21930)

Perf test data(100000 times)
Array: 12.599999997764826ms
String: 1.6000000014901161ms

Perf test case:

```
const permFunctionBodyArray = (rank: number, input: string): string => {
  const reverseFunc = [];
  reverseFunc.push(`fn perm(i: int) -> int {
    var a: int};`);
  for (let i = 0; i < rank; ++i) {
    reverseFunc.push(input);
  }
  reverseFunc.push('return a;}');
  return reverseFunc.join('\n');
};

const permFunctionBodyString = (rank: number, input: string): string => {
  let reverseFunc= `fn perm(i: int}) -> int {
    var a: int;`;
  for (let i = 0; i < rank; ++i) {
    reverseFunc+=input;
  }
  reverseFunc+='return a;}';
  return reverseFunc;//.join('\n');
};
const count = 100000;
let start, end
console.time('array');
start = performance.now();
for(let i =0 ; i < count; i ++) {
    permFunctionBodyArray(3, 'input');
}
end = performance.now();
console.timeEnd('array');
console.log("Array: "+ (end-start));

console.time('string');
start = performance.now();
for(let i =0 ; i < count; i ++) {
    permFunctionBodyString(3, 'input');
}
end = performance.now();
console.log("String: " +(end-start));
console.timeEnd('string');
```

### Description
<!-- Describe your changes. -->



### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->

js/web/lib/wasm/jsep/webgpu/ops/transpose.ts

@@ -26,14 +26,12 @@ const getOutputShape = (inputShape: readonly number[], perm: number[]): readonly
   ShapeUtil.sortBasedOnPerm(inputShape, getAdjustedPerm(inputShape.length, perm));
 
 const permFunctionBody = (perm: number[], rank: number, input: IndicesHelper, output: IndicesHelper): string => {
-  const reverseFunc = [];
-  reverseFunc.push(`fn perm(i: ${output.type.indices}) -> ${input.type.indices} {
-    var a: ${input.type.indices};`);
+  let reverseFunc = `fn perm(i: ${output.type.indices}) -> ${input.type.indices} {
+    var a: ${input.type.indices};`;
   for (let i = 0; i < rank; ++i) {
-    reverseFunc.push(input.indicesSet('a', perm[i], `i[${i}]`));
+    reverseFunc += input.indicesSet('a', perm[i], `i[${i}]`);
   }
-  reverseFunc.push('return a;}');
-  return reverseFunc.join('\n');
+  return (reverseFunc += 'return a;}');
 };
 
 const squeezeShape = (shape: readonly number[], adjustedPerm: number[]): { newShape: number[]; newPerm: number[] } => {