Refactoring and tidy up.

Make the preview manager a singleton (passing in the MXSession to functions). Fix tests.

PreviewManager → URLPreviewManager
URLPreviewViewData → URLPreviewData
URLPreviewCache → URLPreviewStore

Riot/Managers/URLPreviews/URLPreviewData.swift

@@ -0,0 +1,52 @@
+// 
+// Copyright 2021 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Foundation
+
+@objcMembers
+class URLPreviewData: NSObject {
+    /// The URL that's represented by the preview data. This may have been sanitized.
+    /// Note: The original URL, can be found in the bubble components with `eventID` and `roomID`.
+    let url: URL
+    
+    /// The ID of the event that created this preview.
+    let eventID: String
+    
+    /// The ID of the room that this preview is from.
+    let roomID: String
+    
+    /// The OpenGraph site name for the URL.
+    let siteName: String?
+    
+    /// The OpenGraph title for the URL.
+    let title: String?
+    
+    /// The OpenGraph description for the URL.
+    let text: String?
+    
+    /// The OpenGraph image for the URL.
+    var image: UIImage?
+    
+    init(url: URL, eventID: String, roomID: String, siteName: String?, title: String?, text: String?) {
+        self.url = url
+        self.eventID = eventID
+        self.roomID = roomID
+        self.siteName = siteName
+        self.title = title
+        // Remove line breaks from the description text
+        self.text = text?.replacingOccurrences(of: "\n", with: " ")
+    }
+}