Rename Core Data objects.

URLPreviewCacheData becomes URLPreviewData in the model with a class name of URLPreviewDataMO
ClosedURLData becomes URLPreviewUserData in the model with a class name of URLPreviewUserDataMO

Riot/Managers/URLPreviews/Core Data/URLPreviewImageTransformer.swift

@@ -0,0 +1,45 @@
+// 
+// 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 CoreData
+
+/// A `ValueTransformer` for ``URLPreviewCacheData``'s `image` field.
+/// This class transforms between `UIImage` and it's `pngData()` representation.
+class URLPreviewImageTransformer: ValueTransformer {
+    override class func transformedValueClass() -> AnyClass {
+        UIImage.self
+    }
+    
+    override class func allowsReverseTransformation() -> Bool {
+        true
+    }
+    
+    /// Transforms a `UIImage` into it's `pngData()` representation.
+    override func transformedValue(_ value: Any?) -> Any? {
+        guard let image = value as? UIImage else { return nil }
+        return image.pngData()
+    }
+    
+    /// Transforms `Data` into a `UIImage`
+    override func reverseTransformedValue(_ value: Any?) -> Any? {
+        guard let data = value as? Data else { return nil }
+        return UIImage(data: data)
+    }
+}
+
+extension NSValueTransformerName {
+    static let urlPreviewImageTransformer = NSValueTransformerName("URLPreviewImageTransformer")
+}