Add getDefault() and setAll() methods to SpecialFieldsPreferences

- Added private default constructor with default specialFieldsEnabled = true
- Added static getDefault() method to create default preferences
- Added setAll() method to reset preferences from another instance

Fixes #14409

Author: 2400031832

jabgui/src/main/java/org/jabref/gui/specialfields/SpecialFieldsPreferences.java

@@ -13,6 +13,21 @@ public SpecialFieldsPreferences(boolean specialFieldsEnabled) {
         this.specialFieldsEnabled = new SimpleBooleanProperty(specialFieldsEnabled);
     }
 
+    /// Creates object with default values
+    private SpecialFieldsPreferences() {
+        this(
+                true // Default special fields enabled
+        );
+    }
+
+    public static SpecialFieldsPreferences getDefault() {
+        return new SpecialFieldsPreferences();
+    }
+
+    public void setAll(SpecialFieldsPreferences preferences) {
+        this.specialFieldsEnabled.set(preferences.isSpecialFieldsEnabled());
+    }
+
     public boolean isSpecialFieldsEnabled() {
         return specialFieldsEnabled.getValue();
     }