Move IO into a separate module.

builtin/io.wren

@@ -0,0 +1,12 @@
+class IO {
+  static print(obj) {
+    IO.writeString_(obj.toString)
+    IO.writeString_("\n")
+    return obj
+  }
+
+  static write(obj) {
+    IO.writeString_(obj.toString)
+    return obj
+  }
+}