Investigate the possibility of getting rid of ART_EMBED_INTERFACE_EVENT_EMITTER macros

[maratal]

We have ART_EMBED_INTERFACE_EVENT_EMITTER macros that "injects" emitter interface into any class. This solution is not so pretty in comparing of using protocols. Also the idea was to use together with ART_EMBED_IMPLEMENTATION_EVENT_EMITTER, but that was never implemented.

Originates from internal discussion.

┆Issue is synchronized with this Jira Task by Unito

[maratal]

Looks like current approach is better than what can be done with protocols in Objective-c. Currently we have generic event emitters like ARTEventEmitter<ARTEvent *, ARTConnectionStateChange *>. But once ARTEventEmitterProtocol introduced, emitters stop to be generic which hugely disrupts the whole code base as well as the test suite (and makes it less convenient).

See 2179-research branch for details.