This patch renames `RoomEventCacheUpdate::UpdateReadMarker` to
`ReadMarker`. The `Update` prefix is already part of the enum name.

…ve_to`.

This patch renames `RoomEventCacheUpdate::ReadMarker::event_id` to
`ReadMarker::move_to` as I feel like it conveys a better semantics.

This patch extracts `RoomEventCacheUpdate::Append::ambiguity_changes`
into a new variant `RoomEventCacheUpdate::Members { ambiguity_changes }
`.

This patch also creates a new private
`RoomEventCacheInner::send_grouped_updates_for_events` method to ensure
the updates are sent in a particular order.

This patch renames `RoomEventCacheUpdate::Append` to `SyncEvents`. The
field `events` is renamed `timeline`.

This patch also renames some variables to clarify the code and to match
the renamings in `RoomEventCacheUpdate`.

This patch renames `ReadMarker { move_to: … }` to `MoveReaderMarkerTo
{ event_id: … }`.

This patch also renames `Members` to `UpdateMembers`.

Finally, this patch renames some other variables to avoid clashes with
terminology in `matrix_sdk_ui`.

This patch splits `RoomEventCacheUpdate::SyncEvents` into 2 new variants:
`AddTimelineEvents` and `AddEphemeralEvents`.

This patch takes this opportunity to update `matrix_sdk_ui::timeline`
a little bit too. `handle_sync_events` is renamed
`handle_ephemeral_events`, and the `SyncTimelineEvent` argument is
removed: it's possible to use `add_events_at` directly to handle the
`SyncTimelineEvent`s.

This patch prevents sending useless `RoomEventCacheUdpate` if their
respective values are empty.

Signed-off-by: Benjamin Bouvier <[email protected]>