multi-cursor: wip: track cursor shapes and colors

And erase all extra cursors on reset, resize and clear
screen/scrollback (ED 2/3).

render.c

@@ -4812,6 +4812,8 @@ render_resize(struct terminal *term, int width, int height, uint8_t opts)
 
     term->render.last_cursor.row = NULL;
 
+    term_remove_all_multi_cursors(term);
+
 damage_view:
     /* Signal TIOCSWINSZ */
     send_dimensions_to_client(term);