TEXT SAVE: If file already exists then warn before overwriting

[gjwgit]

Is there some reason why we use both file_picker and file_selector? If file picker is the better, then let's use that.

Closing Criteria

• Please migrate to using file_picker rather than file_selector.

Details

These two use file_selector

lib/features/wordcloud/config.dart:import 'package:file_selector/file_selector.dart' as fs;
lib/utils/save_dataset_button.dart:import 'package:file_selector/file_selector.dart' as fs;

We are using file_picker everywhere else:

lib/widgets/text_page.dart:import 'package:file_picker/file_picker.dart';
lib/widgets/close_dialog.dart:import 'package:file_picker/file_picker.dart';
lib/features/dataset/file_folder_picker.dart:import 'package:file_picker/file_picker.dart';
lib/features/dataset/file_folder_picker.dart: // Use file_picker package to select folder.
lib/tabs/script/save_button.dart:import 'package:file_picker/file_picker.dart';
lib/utils/select_file.dart:import 'package:file_picker/file_picker.dart';