Provide a way to "inject" providers into a ProviderScope/ProviderContainer

[iapicca]

use case

I initialize my app while holding the splash screen up and most importantly before runApp

code sample

void main() async {
FlutterError.demangleStackTrace = (stack) {
  if (stack is stack_trace.Trace) {
    return stack.vmTrace;
  }
  if (stack is stack_trace.Chain) {
    return stack.toTrace().vmTrace;
  }
  return stack;
};

final widgetsBinding = WidgetsFlutterBinding.ensureInitialized();
web.usePathUrlStrategy();
FlutterNativeSplash.preserve(widgetsBinding: widgetsBinding);

final container = ProviderContainer();
final initializer = container.read(initializeApplicationProvider);

final result = await initializer();
if (result.isFailure) {
  exit(0);
}

widgetsBinding.scheduleAttachRootWidget(
  widgetsBinding.wrapWithDefaultView(
    ProviderScope(
      parent: container,
      child: const Application(),
    ),
  ),
);

await Future.microtask(widgetsBinding.scheduleWarmUpFrame);
FlutterNativeSplash.remove();
}

problem

ProviderScope parent will get deprecated (see issue 3261)

proposal

provide a way to inject in ProviderScope the providers from a ProviderContainer

[rrousselGit]

Use UncontrolledProviderScope here