reorg: move JS ops implementations to cli/js/ops/, part 3 (#4302)

Following JS ops were moved to separate files in cli/js/ops directory:
- net
- tls
- fs

cli/js/ops/fs/dir.ts

@@ -0,0 +1,27 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+import { sendSync } from "../dispatch_json.ts";
+
+/**
+ * **UNSTABLE**: maybe needs permissions.
+ *
+ * Return a string representing the current working directory.
+ *
+ * If the current directory can be reached via multiple paths (due to symbolic
+ * links), `cwd()` may return any one of them.
+ *
+ * Throws `Deno.errors.NotFound` if directory not available.
+ */
+export function cwd(): string {
+  return sendSync("op_cwd");
+}
+
+/**
+ * **UNSTABLE**: maybe needs permissions.
+ *
+ * Change the current working directory to the specified path.
+ *
+ * Throws `Deno.errors.NotFound` if directory not available.
+ */
+export function chdir(directory: string): void {
+  sendSync("op_chdir", { directory });
+}