feat: add exit_listen func to stop listening

[Pranav2612000]

What does this PR do?

• Adds an exit_listen function similar to exit_grab to stop listening for events

[rustdesk]

@fufesou

[fufesou]

This PR works fine. It is OK to stop and start again and again.

As methioned above, exit_listen is similar to exit_grab.

rdev/src/macos/grab.rs

Line 78 in a90dbe1

pub fn exit_grab() -> Result<(), GrabError> {

NOTE: RustDesk does not use listen(), it uses grab().