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/RoomScreenViewModel.swift

@@ -52,7 +52,7 @@ class RoomScreenViewModel: RoomScreenViewModelType, RoomScreenViewModelProtocol
                                                          timelineStyle: appSettings.timelineStyle,
                                                          readReceiptsEnabled: appSettings.readReceiptsEnabled,
                                                          isEncryptedOneToOneRoom: roomProxy.isEncryptedOneToOneRoom,
-                                                         bindings: .init(composerText: "", composerFocused: false)),
+                                                         bindings: .init(composerText: "", composerFocused: false, reactionsCollapsed: [:])),
                    imageProvider: mediaProvider)
 
         setupSubscriptions()
@@ -656,6 +656,19 @@ private extension RoomProxyProtocol {
     }
 }
 
+extension RoomScreenViewModel.Context {
+    /// A function to make it easier to bind to reactions expand/collapsed state
+    /// - Parameter itemID: The id of the timeline item the reacted to
+    /// - Returns: Wether the reactions should show in the collapsed state, true by default.
+    func reactionsCollapsedBinding(for itemID: String) -> Binding<Bool> {
+        Binding(get: {
+            self.reactionsCollapsed[itemID] ?? true
+        }, set: {
+            self.reactionsCollapsed[itemID] = $0
+        })
+    }
+}
+
 // MARK: - Mocks
 
 extension RoomScreenViewModel {