Enable PreDH format in the deck editor (#5282)

* - PreDH: Avoid warnings, exclude some sets that aren't yet in Forge

* - Enable PreDH format as always available to the player.

forge-game/src/main/java/forge/game/GameFormat.java

@@ -367,6 +367,7 @@ public class GameFormat implements Comparable<GameFormat> {
             coreFormats.add("Oathbreaker.txt");
             coreFormats.add("Premodern.txt");
             coreFormats.add("Pauper.txt");
+            coreFormats.add("PreDH.txt");
         }
         
         public Reader(File forgeFormats, File customFormats, boolean includeArchived) {