envelopes: code expects serialized events in JSON format, not envelopes

[rhcarvalho]

As pointed out by @dashed:

sentry-javascript/packages/browser/src/integrations/breadcrumbs.ts

Lines 310 to 331 in 2efbc98

	/**
	* Create a breadcrumb of `sentry` from the events themselves
	*/
	function addSentryBreadcrumb(serializedData: string): void {
	// There's always something that can go wrong with deserialization...
	try {
	const event = JSON.parse(serializedData);
	getCurrentHub().addBreadcrumb(
	{
	category: `sentry.${event.type === 'transaction' ? 'transaction' : 'event'}`,
	event_id: event.event_id,
	level: event.level || Severity.fromString('error'),
	message: getEventDescription(event),
	},
	{
	event,
	},
	);
	} catch (_oO) {
	logger.error('Error while adding sentry type breadcrumb');
	}
	}

We have code to add breadcrumbs that take serialized data as input. That function does not understand envelopes.