[SDK-4009] Refactoring presence

[maratal]

Closes #1875

See commit messages on what goes where.

[sacOO7]

I feel most of the presence specific code is still defined under Source/ARTRealtimeChannel.m. It should be moved under Source/ARTRealtimePresence.m. Some of those methods are sync, onsync and onPresence. Also, part of the code under setAttached should be moved to Source/ARTRealtimePresence.m as an individual method.

Can you please refer to https://github.com/ably/ably-go/blob/main/ably/realtime_channel.go file to check what should be defined under ARTRealtimeChannel.m file

[lawrence-forooghian]

These changes alone don't seem to resolve #1848; the PR doesn’t "re-enable presence tests", nor “go through the current presence implementation and check if it's compatible with spec” (although I'm not really sure what @sacOO7 had in mind when he wrote the latter; was there some reason to believe that we are not conforming to the spec)?

[maratal]

These changes alone don't seem to resolve #1848; the PR doesn’t "re-enable presence tests", nor “go through the current presence implementation and check if it's compatible with spec” (although I'm not really sure what @sacOO7 had in mind when he wrote the latter; was there some reason to believe that we are not conforming to the spec)?

I've changed the issue to #1875.

[lawrence-forooghian]

Changes look good to me — will let @sacOO7 say what other changes he'd like to see as part of this refactor.

[maratal]

Changes look good to me — will let @sacOO7 say what other changes he'd like to see as part of this refactor.

I'm working on it - move all code with self.presence... into presence object.

[sacOO7]

Few more refactorings to be done

[sacOO7]

LGTM