The event types are a bit of a mess I think. For bindings it would be good to
know if a given type of message is upstream, downstream, serialized etc, which
requires the event type to have flags, but now they are wrapped as enums. Which
makes sense ("eos" is a better answer to "which kind of event is this" than "eos
| serialized | downstream"), but lacks something. I suspect that we need to
tweak the types a bit, so that EventType remains an enum, but there is a
function or macro gst_event_type_get_flags, which returns a EventTypeFlags.