Add user suggestions for @room. (#7453)

RiotSwiftUI/Modules/Room/UserSuggestion/Service/UserSuggestionService.swift

@@ -23,7 +23,13 @@ struct RoomMembersProviderMember {
     var avatarUrl: String
 }
 
+class UserSuggestionID: NSObject {
+    /// A special case added for suggesting `@room` mentions.
+    @objc static let room = "@room"
+}
+
 protocol RoomMembersProviderProtocol {
+    var canMentionRoom: Bool { get }
     func fetchMembers(_ members: @escaping ([RoomMembersProviderMember]) -> Void)
 }
 
@@ -100,7 +106,7 @@ class UserSuggestionService: UserSuggestionServiceProtocol {
                 return
             }
             
-            self.suggestionItems = members.map { member in
+            self.suggestionItems = members.withRoom(self.roomMemberProvider.canMentionRoom).map { member in
                 UserSuggestionServiceItem(userId: member.userId, displayName: member.displayName, avatarUrl: member.avatarUrl)
             }
             
@@ -113,3 +119,11 @@ class UserSuggestionService: UserSuggestionServiceProtocol {
         }
     }
 }
+
+extension Array where Element == RoomMembersProviderMember {
+    /// Returns the array with an additional member that represents an `@room` mention.
+    func withRoom(_ canMentionRoom: Bool) -> Self {
+        guard canMentionRoom else { return self }
+        return self + [RoomMembersProviderMember(userId: UserSuggestionID.room, displayName: "Everyone", avatarUrl: "")]
+    }
+}