Dead Player's shouldn't be able to move

This fixes a lot of game state issues where packets were delayed for processing
due to 1.15's new queue but processed while dead.

paper-server/patches/sources/net/minecraft/world/entity/player/Player.java.patch

@@ -268,7 +268,7 @@
      }
  
      public boolean isTextFilteringEnabled() {
-@@ -1061,7 +1134,13 @@
+@@ -1061,13 +1134,19 @@
  
      @Override
      public void removeVehicle() {
@@ -283,6 +283,13 @@
          this.boardingCooldown = 0;
      }
  
+     @Override
+     protected boolean isImmobile() {
+-        return super.isImmobile() || this.isSleeping();
++        return super.isImmobile() || this.isSleeping() || this.isRemoved() || !valid; // Paper - player's who are dead or not in a world shouldn't move...
+     }
+ 
+     @Override
 @@ -1144,10 +1223,15 @@
  
                  f *= 0.2F + f2 * f2 * 0.8F;