[Breaking change] Language Picker API Improvements

[StanevPrime]

As a developer I want to have an ease to use API of the чshowChangeLanguageBottomSheetч so that I can integrate that component with a minimal effort.

ACs

• All icons to be moved from the widget constructor to the theme extension
• Add an item builder closure
• Update the documentation
  • Add an example with the minimal configuration
  • Add an example with the full configuration
  • Add example of the LanguageService implementation (similar to this doc)
• Update the package version as well as the CHANGELOG

Current API

void showChangeLanguageBottomSheet({
  required BuildContext context,
  Widget Function(ErrorModel?)? errorBuilder,
  required Widget Function(BuildContext)? headerBuilder,
  dynamic iconRight,
  LanguagePickerConfiguration configuration = const LanguagePickerConfiguration(),
  final MessagePanelState messageState = MessagePanelState.important,
  dynamic errorPanelIcon,
})

Improved API

void showChangeLanguageBottomSheet({
  required BuildContext context,
  required Function(LanguageModel language) onChanged,
  required Function(LanguageModel language) translate,
  required LanguageService service,
  Widget Function(BuildContext)? headerBuilder,
  Widget Function(ErrorModel?)? errorBuilder,
  Widget Function(SelectedLanguageModel model, bool loading)? itemBuilder,
  LanguagePickerConfiguration configuration = const LanguagePickerConfiguration(),
  MessagePanelState messageState = MessagePanelState.important,
})

Theme extension

 ...
  dynamic iconRight,
  dynamic errorPanelIcon,