Better hidden folders display preferences for editor file dialogs
Created by: ghost
Small improvements for file dialogs:
- By default FileDialog and EditorFileDialog don't show hidden folders as, by default, is set as false in the editor settings. https://github.com/godotengine/godot/blob/master/tools/editor/editor_settings.cpp#L517
- EditorFileDialog hidden folders visibility can be toggled using editor settings "file_dialog/show_hidden_folders" option.
Closes #2041 (closed).