chore(sdk): Rename and split a couple of types in latest_event.

This patch splits the `LatestEventValue` type into `LatestEventValue`
+ `LatestEventKind`. Basically, all variants in `LatestEventValue` are
moved inside the new `LatestEventKind` enum. `LatestEventValue` keeps
`None`, and see the new `Remote`, `LocalIsSending` and `LocalIsWedged`
variants.

This patch also extracts the message-like handling of `find_and_map`
(now renamed `find_and_map_timeline_event`) into its own function:
`find_and_map_any_message_like_event_content`. This is going to be
handful for the send queue part.

Author: Hywan