Add reference page for isSoundPlaying() (#5868)

* add a reference page for 'is-sound-playing'

* update help path for api

* fix snippet

docs/reference/music/is-sound-playing.md

@@ -0,0 +1,40 @@
+# is Sound Playing
+
+Check if sound is playing at any sound output.
+
+```sig
+music.isSoundPlaying()
+```
+
+### ~ reminder
+
+![works with micro:bit V2 only image](/static/v2/v2-only.png)
+
+This function requires the [micro:bit V2](/device/v2) hardware. If you use this function with a micro:bit v1 board, you will see the **927** error code on the screen.
+
+### ~
+
+Sound is played at the built-in speaker or at the selected audio output pin. You can check if any sound is currently being played at any of these outputs.
+
+## Returns
+
+* a [boolean](/types/boolean) value that is `true` if sound is being played at the built-in speaker or at the audio pin. The value is `false` otherwise.
+
+## Example #example
+
+Stop all sounds if any are currently playing.
+
+```blocks
+if (music.isSoundPlaying()) {
+    music.stopAllSounds()
+}
+```
+
+## See also
+
+[set built-in speaker enabled](/reference/music/set-built-in-speaker-enabled),
+[set audio pin](/reference/pins/set-audio-pin)
+
+```package
+music
+```

libs/core/music.cpp

@@ -68,7 +68,7 @@ void setBuiltInSpeakerEnabled(bool enabled) {
 */
 //% blockId=music_sound_is_playing block="sound is playing"
 //% group="micro:bit (V2)"
-//% help=music/volume
+//% help=music/is-sound-playing
 //% weight=0
 bool isSoundPlaying() {
 #if MICROBIT_CODAL