New timeline (#276) (#280)

* 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

ElementX/Sources/Other/HTMLParsing/AttributedStringBuilder.swift

@@ -21,13 +21,7 @@ struct AttributedStringBuilder: AttributedStringBuilderProtocol {
     private let temporaryBlockquoteMarkingColor = UIColor.magenta
     private let temporaryCodeBlockMarkingColor = UIColor.cyan
     private let linkColor = UIColor.blue
-    
-    func fromPlain(_ string: String?) async -> AttributedString? {
-        await Task.dispatch(on: .global()) {
-            fromPlain(string)
-        }
-    }
-    
+        
     func fromPlain(_ string: String?) -> AttributedString? {
         guard let string else {
             return nil
@@ -39,13 +33,7 @@ struct AttributedStringBuilder: AttributedStringBuilderProtocol {
         
         return try? AttributedString(mutableAttributedString, including: \.elementX)
     }
-    
-    func fromHTML(_ htmlString: String?) async -> AttributedString? {
-        await Task.dispatch(on: .global()) {
-            fromHTML(htmlString)
-        }
-    }
-    
+        
     // Do not use the default HTML renderer of NSAttributedString because this method
     // runs on the UI thread which we want to avoid because renderHTMLString is called
     // most of the time from a background thread.