Allow /player spawn spawn offline-mode player in online server; Code clean-up in /player spawn command (#872)

* Clean up code in PlayerCommand.spawn and EntityPlayerMPFake.createFake.

* Update src/main/java/carpet/CarpetSettings.java

* Update src/main/java/carpet/commands/PlayerCommand.java

* Update src/main/java/carpet/patches/EntityPlayerMPFake.java

Co-authored-by: gnembon <41132274+gnembon@users.noreply.github.com>

src/main/java/carpet/CarpetSettings.java

@@ -472,6 +472,9 @@ public class CarpetSettings
     @Rule(desc = "Enables /player command to control/spawn players", category = COMMAND)
     public static String commandPlayer = "ops";
 
+    @Rule(desc = "Spawn offline players in online mode if online-mode player with specified name does not exist", category = COMMAND)
+    public static boolean allowSpawningOfflinePlayers = true;
+
     @Rule(desc = "Allows to track mobs AI via /track command", category = COMMAND)
     public static String commandTrackAI = "ops";