Redo logic around note selection, add new buttons for selecting individual sides.

source/funkin/ui/debug/charting/commands/ExtendNoteLengthCommand.hx

@@ -45,6 +45,12 @@ class ExtendNoteLengthCommand implements ChartEditorCommand
     state.sortChartData();
   }
 
+  public function shouldAddToHistory(state:ChartEditorState):Bool
+  {
+    // This command is undoable. Add to the history if we actually performed an action.
+    return (oldLength != newLength);
+  }
+
   public function toString():String
   {
     return 'Extend Note Length';