patch 8.1.1335: listener callback is called after inserting text

Problem:    Listener callback is called after inserting text.
Solution:   Flush the changes before inserting or deleting a line.  Store
            changes per buffer.

src/structs.h

@@ -2439,6 +2439,7 @@ struct file_buffer
     dict_T	*b_vars;	/* internal variables, local to buffer */
 
     listener_T	*b_listener;
+    list_T	*b_recorded_changes;
 #endif
 #ifdef FEAT_TEXT_PROP
     int		b_has_textprop;	// TRUE when text props were added