perf: avoid buffer cloning (#3264)

Author: tsctx

lib/web/fetch/body.js

@@ -392,7 +392,7 @@ function bodyMixinMethods (instance) {
       // with this and the following step given a byte sequence bytes: return the
       // result of creating a Uint8Array from bytes in this’s relevant realm.
       return consumeBody(this, (bytes) => {
-        return new Uint8Array(bytes)
+        return new Uint8Array(bytes.buffer, 0, bytes.byteLength)
       }, instance, true)
     }
   }