Add expand/collapse UI for reactions (#1249)

* Add expand/collapse UI for reactions

- Adds a CollapsibleFlowLayout for controlling the layout
- Adds tests for  this layout and some mocks for testing layouts generally
- Improves the rendering of the reaction buttons which were not pixel perfect
- Adds the UI for the expand collapse buttons including the count of hidden items in the collapsed state.

* Add comment for reactionsCollapsed binding.

* Remove Flow and simplify implementation

- Remove SwiftUI-Flow
- Add strings by importing from Localyse
- Remove count on expand button as requires GeometryReader and can cause loops
- Don't use GeometryReader for hiding reactions with opacity(just put them way off screen for now)
- Fix unit and UI tests

* Address PR comments

- use synthesized inits
- use rows rather than lines for naming flow layout
- other naming improvements
- reactions were already rendered in another ui test, removing my test on favour of those and updating the screenshots for those.

ElementX/Sources/Screens/RoomScreen/RoomScreenModels.swift

@@ -127,6 +127,10 @@ struct RoomScreenViewStateBindings {
         }
     }
     
+    /// The state of wether reactions listed on the timeline are expanded/collapsed.
+    /// Key is itemID, value is the collapsed state.
+    var reactionsCollapsed: [String: Bool]
+    
     /// A media item that will be previewed with QuickLook.
     var mediaPreviewItem: MediaPreviewItem?