Exception withContext is overwritten by native scope sync

[krystofwoldrich]

Description

Expected:

This code should capture the exception with extra breadcrumb.

    await Sentry.captureException(error, stackTrace: stackTrace, withScope: (scope) {
      scope.addBreadcrumb(Breadcrumb(message: 'breadcrumb from with scope'));
    });

Actual:

The breadcrumb is missing.

Culprit:

sentry-dart/flutter/lib/src/integrations/load_contexts_integration.dart

Lines 151 to 166 in cd16818

	final breadcrumbsList = infos['breadcrumbs'] as List?;
	if (breadcrumbsList != null &&
	breadcrumbsList.isNotEmpty &&
	_options.enableScopeSync) {
	final breadcrumbsJson =
	List<Map<dynamic, dynamic>>.from(breadcrumbsList);
	final breadcrumbs = <Breadcrumb>[];
	for (final breadcrumbJson in breadcrumbsJson) {
	final breadcrumb = Breadcrumb.fromJson(
	Map<String, dynamic>.from(breadcrumbJson),
	);
	breadcrumbs.add(breadcrumb);
	}
	event = event.copyWith(breadcrumbs: breadcrumbs);
	}

Notes:
The local exception scope is overridden by the one we fetch from the native SDKs. Scope fetched from a native SDK contains both Flutter and Native data. We shouldn't introduce duplicates.

[krystofwoldrich]

Related issue in RN getsentry/sentry-react-native#2146