Give serializers flexibility to map based on event type

[aidan-casey]

Hey there!

The current serializer interface requires that the implementation keep track of the event class when serializing.

For example:

{
	"class": "MyOrg\\CRM\\Contact\\ContactWasCreated",
	"payload": {...}
}

It is traditionally better practice to remove references to the class in the event store and have this mapped during deserialization. Handling serialization this way also ensures some ability to work with these events across multiple systems (and languages).

However, we would have to introduce some breaking changes to facilitate this.

• The serializer now needs to be conscious of the event type.
• The metadata serializer may need to become a separate interface.
• We need to introduce an additional interface for event-type mapping.

I am happy to start looking into implementing these features, but I wanted to probe whether it would be something that you would accept, given the breaking changes it introduces.