Clean up manga restoring logic

Some behavior changes:
- It prioritizes new entries, then anything more recently updated
- It copies the more recently updated entry's metadata (description, thumbnail, etc.)

(cherry picked from commit 58daedc89ee18d04e7af5bab12629680dba4096c)

# Conflicts:
#	app/src/main/java/eu/kanade/tachiyomi/data/backup/BackupRestorer.kt
#	app/src/main/java/eu/kanade/tachiyomi/source/model/SMangaExtensions.kt

data/src/main/sqldelight/tachiyomi/data/mangas.sq

@@ -78,6 +78,10 @@ getAllManga:
 SELECT *
 FROM mangas;
 
+getAllMangaSourceAndUrl:
+SELECT source, url
+FROM mangas;
+
 getMangasWithFavoriteTimestamp:
 SELECT *
 FROM mangas