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/timers.ts

@@ -8,3 +8,12 @@ export function stopGlobalTimer(): void {
 export async function startGlobalTimer(timeout: number): Promise<void> {
   await sendAsync("op_global_timer", { timeout });
 }
+
+interface NowResponse {
+  seconds: number;
+  subsecNanos: number;
+}
+
+export function now(): NowResponse {
+  return sendSync("op_now");
+}