feat(Refactoring): Added const constructor

Author: Coloud1

lib/app/util/formatters/first_character_is_not_digit_formatter.dart

@@ -1,6 +1,8 @@
 import 'package:flutter/services.dart';
 
 class FirstCharacterNotDigitFormatter extends TextInputFormatter {
+  const FirstCharacterNotDigitFormatter();
+
   @override
   TextEditingValue formatEditUpdate(
     TextEditingValue oldValue,

lib/presentation/screen/screens_screen/widgets/add_screen_dialog.dart

@@ -96,7 +96,7 @@ class _AddScreenDialogState extends State<AddScreenDialog> {
                     onSubmitted: (_) => _onOk(context),
                     placeholder: S.of(context).screenName,
                     inputFormatters: [
-                      FirstCharacterNotDigitFormatter(),
+                      const FirstCharacterNotDigitFormatter(),
                       FilteringTextInputFormatter.allow(
                         AppConsts.digitsAndLatinLetters,
                       ),