Add a way to toggle AudioSink (bevyengine#6321)

# Objective

Currently toggling an `AudioSink` (for example from a game menu) requires writing

```rs
if sink.is_paused() {
    sink.play();
} else {
    sink.pause();
}
```

It would be nicer if we could reduce this down to a single line

```rs
sink.toggle();
```

## Solution

Add an `AudioSink::toggle` method which does exactly that.

---

## Changelog

- Added `AudioSink::toggle` which can be used to toggle state of a sink.

crates/bevy_audio/src/audio_output.rs

@@ -178,9 +178,20 @@ impl AudioSink {
         self.sink.as_ref().unwrap().pause();
     }
 
+    /// Toggles the playback of this sink.
+    ///
+    /// Will pause if playing, and will be resumed if paused.
+    pub fn toggle(&self) {
+        if self.is_paused() {
+            self.play();
+        } else {
+            self.pause();
+        }
+    }
+
     /// Is this sink paused?
     ///
-    /// Sinks can be paused and resumed using [`pause`](Self::pause) and [`play`](Self::play).
+    /// Sinks can be paused and resumed using [`pause`](Self::pause), [`play`](Self::play), and [`toggle`](Self::toggle).
     pub fn is_paused(&self) -> bool {
         self.sink.as_ref().unwrap().is_paused()
     }

examples/audio/audio_control.rs

@@ -43,11 +43,7 @@ fn pause(
 ) {
     if keyboard_input.just_pressed(KeyCode::Space) {
         if let Some(sink) = audio_sinks.get(&music_controller.0) {
-            if sink.is_paused() {
-                sink.play();
-            } else {
-                sink.pause();
-            }
+            sink.toggle();
         }
     }
 }