* Fixes#276 - Rebuilt room timeline:
- Removed the need for the ListCollectionViewAdapter
- Rewrote the TimelineItemList without using introspection
- Added ReversedScrollView for laying out items at the bottom/trailing
- Rewrote TimelineProvider diffing through CollectionDifference (similar to the RoomSummaryProvider)
- Added back `scrollDismissesKeyboard` behavior
- Various other tweaks and fixes
- Fixed various warnings:
- removed async AttributedStringBuilder as AttributedString is non-sendable, made the RoomTimelineItemFactory synchronous
- removed unused virtual timeline items
- removed unused isOutgoing property from the FormattedBodyText
* Make TimelineItemContextMenuActions indentifiable and specify contextMenu identifiers
* Bump the matrix-rust-components-swift to v1.0.16-alpha
* Add changes file and changelog contribution guide
* Fix attributed string builder unit tests
