feat(mobile): exclude locales from overpass font (#14158)

* feat(mobile): create localeProvider

This provider can be used to refresh providers that provide UI elements
and get cached.

* feat(mobile): use default font for locales not supported by Overpass

* chore(mobile): fix test

* refactor(mobile): use Locale instead of String

mobile/lib/providers/locale_provider.dart

@@ -0,0 +1,4 @@
+import 'package:flutter/widgets.dart';
+import 'package:hooks_riverpod/hooks_riverpod.dart';
+
+final localeProvider = Provider<Locale>((_) => throw UnimplementedError());