Add TextDecoder benchmark (#3180)

cli/tests/text_decoder_perf.js

@@ -0,0 +1,38 @@
+const mixed = new TextEncoder().encode("@Ā๐😀");
+
+function generateRandom(bytes) {
+  const result = new Uint8Array(bytes);
+  let i = 0;
+  while (i < bytes) {
+    const toAdd = Math.floor(Math.random() * Math.min(4, bytes - i));
+    switch (toAdd) {
+      case 0:
+        result[i] = mixed[0];
+        i++;
+        break;
+      case 1:
+        result[i] = mixed[1];
+        result[i + 1] = mixed[2];
+        i += 2;
+        break;
+      case 2:
+        result[i] = mixed[3];
+        result[i + 1] = mixed[4];
+        result[i + 2] = mixed[5];
+        i += 3;
+        break;
+      case 3:
+        result[i] = mixed[6];
+        result[i + 1] = mixed[7];
+        result[i + 2] = mixed[8];
+        result[i + 3] = mixed[9];
+        i += 4;
+        break;
+    }
+  }
+  return result;
+}
+
+const randomData = generateRandom(1024);
+const decoder = new TextDecoder();
+for (let i = 0; i < 10_000; i++) decoder.decode(randomData);