perf(ext/headers): optimize getHeader using for loop (#20115)

This PR optimizes the `getHeader` function by replacing `.filter` and
`.map` with a `for` loop

**this patch**

```
cpu: 13th Gen Intel(R) Core(TM) i9-13900H
runtime: deno 1.36.0 (x86_64-unknown-linux-gnu)

benchmark        time (avg)        iter/s             (min … max)       p75       p99      p995
----------------------------------------------------------------- -----------------------------
Headers.get      132.2 ns/iter   7,564,093.4 (125.81 ns … 147.66 ns) 133.79 ns 144.92 ns 145.36 ns
```

**main**

```
cpu: 13th Gen Intel(R) Core(TM) i9-13900H
runtime: deno 1.36.0 (x86_64-unknown-linux-gnu)

benchmark        time (avg)        iter/s             (min … max)       p75       p99      p995
----------------------------------------------------------------- -----------------------------
Headers.get     191.48 ns/iter   5,222,523.6 (182.75 ns … 212.22 ns)  193.5 ns 205.96 ns 211.51 ns
```

```js

const headers = new Headers({
  "Content-Type": "application/json",
  "Date": "Thu, 10 Aug 2023 07:45:10 GMT",
  "X-Deno": "Deno",
  "Powered-By": "Deno",
  "Content-Encoding": "gzip",
  "Set-Cookie": "__Secure-ID=123; Secure; Domain=example.com",
  "Content-Length": "150",
  "Vary": "Accept-Encoding, Accept, X-Requested-With",
});

Deno.bench("Headers.get", () => {
  const i = headers.get("x-deno");
});
```

1 files changed, 7 insertions, 9 deletions

diff --git a/ext/fetch/20_headers.js b/ext/fetch/20_headers.js
index 45bd29ad3..fabd39c0e 100644
--- a/ext/fetch/20_headers.js
+++ b/ext/fetch/20_headers.js
@@ -22,12 +22,10 @@ import {
 const primordials = globalThis.__bootstrap.primordials;
 const {
   ArrayIsArray,
-  ArrayPrototypeMap,
   ArrayPrototypePush,
   ArrayPrototypeSort,
   ArrayPrototypeJoin,
   ArrayPrototypeSplice,
-  ArrayPrototypeFilter,
   ObjectEntries,
   ObjectHasOwn,
   RegExpPrototypeExec,
@@ -162,13 +160,13 @@ function appendHeader(headers, name, value) {
  */
 function getHeader(list, name) {
   const lowercaseName = byteLowerCase(name);
-  const entries = ArrayPrototypeMap(
-    ArrayPrototypeFilter(
-      list,
-      (entry) => byteLowerCase(entry[0]) === lowercaseName,
-    ),
-    (entry) => entry[1],
-  );
+  const entries = [];
+  for (let i = 0; i < list.length; i++) {
+    if (byteLowerCase(list[i][0]) === lowercaseName) {
+      ArrayPrototypePush(entries, list[i][1]);
+    }
+  }
+
   if (entries.length === 0) {
     return null;
   } else {