v2.6.1: Fix #21980 and #21902

* #21902: IAE: Listener was not registered before

  This is caused by (a) sharing an action between a menu and (b) a
  mapframe icon.

  This adds a non-regression test, and additionally modifies the
  AreaSelectorAction to override `readPreferences`, which is called
  when the map mode is entered. Furthermore, the MapMode class implements
  PreferenceChangedListener, which removes the need to notify the
  action manually about modified preferences.

* #21980: PreferencePanel: Fix an NPE

  This occurs when TaggingPreset#getRawName returns null, which occurs
  with TaggingPresetSeparator. This patch ignores TaggingPresetSeparator
  and uses Objects#equals.