Add onCloseSubState script event to MusicBeatSubstate

[richTrash21]

Adds onCloseSubState script event for MusicBeatSubstates. Basicaly #789 but for substates lol

[ItsLJcool]

yes this would be nice... if only there was an onClose event callback because this is already implemented
https://github.com/CodenameCrew/CodenameEngine/blob/main/source/funkin/backend/MusicBeatSubstate.hx#L161

[ItsLJcool]

the only reason I added it into MusicBeatState because there was no physical event that was called when the SubState closed. This is not true for the MusicBeatSubState. This does prove useful however for substate substates, so I still think it's a valid pr

[richTrash21]

This does prove useful however for substate substates

Thats why I made this pr! I'm using onOpenSubState/onCloseSubState to turn on/off mouse events on menu buttons and one of the menus is a substate... that can open other substate menu. 😅😅