Fix Kingfisher deprecation warnings (#2799)

Task/Issue URL: https://app.asana.com/0/414235014887631/1207185436384594/f
Tech Design URL:
CC:

Description:

This PR fixes Kingfisher deprecation warnings.

These appear on every PR, like this one, where you can see a list of warnings at the bottom of the diff.

Core/FaviconsHelper.swift

@@ -24,11 +24,11 @@ struct FaviconsHelper {
 
     // this function is now static and outside of Favicons, otherwise there is a circular dependency between
     // Favicons and NotFoundCachingDownloader
-    public static func defaultResource(forDomain domain: String?, sourcesProvider: FaviconSourcesProvider) -> Kingfisher.ImageResource? {
+    public static func defaultResource(forDomain domain: String?, sourcesProvider: FaviconSourcesProvider) -> KF.ImageResource? {
         guard let domain = domain,
               let source = sourcesProvider.mainSource(forDomain: domain) else { return nil }
 
         let key = Favicons.createHash(ofDomain: domain)
-        return ImageResource(downloadURL: source, cacheKey: key)
+        return KF.ImageResource(downloadURL: source, cacheKey: key)
     }
 }

DuckDuckGo/Favicons.swift

@@ -441,7 +441,7 @@ public class Favicons {
         return image
     }
 
-    public func defaultResource(forDomain domain: String?) -> Kingfisher.ImageResource? {
+    public func defaultResource(forDomain domain: String?) -> KF.ImageResource? {
         return FaviconsHelper.defaultResource(forDomain: domain, sourcesProvider: sourcesProvider)
     }