App polish part 2 (#1118)

- Fix sheet backgrounds in dark mode.
- Fix background colours for reaction buttons.
- Reply view layout.
- Update separator colours.
- Don't show sender name/avatar in DMs.
- Fix inconsistent line heights with formatted body text.
- Use plain text for reply
- Increase tappable size of collapsed state changes button.
- Blockquote layout and text colour.
- Tap to expand the topic in room details.
- Change the topic and security font size in room details.
- Add cancel button when inviting someone to an existing room.
- Reword Add Friends to Add People in start chat screen.
- Update compound.

ElementX/Sources/Screens/StartChatScreen/StartChatScreenCoordinator.swift

@@ -97,6 +97,8 @@ final class StartChatScreenCoordinator: CoordinatorProtocol {
             guard let self else { return }
             
             switch result {
+            case .cancel:
+                break // Not shown in this flow.
             case .proceed:
                 openCreateRoomScreen()
             case .invite: