feat: add placeholder for plot size

- PlaceholderRegistry and for /plot list entries
 - fixes #4149

Core/src/main/java/com/plotsquared/core/command/ListCmd.java

@@ -517,6 +517,7 @@ public class ListCmd extends SubCommand {
                     }
                 }
                 finalResolver.tag("players", Tag.inserting(builder.asComponent()));
+                finalResolver.tag("size", Tag.inserting(Component.text(plot.getConnectedPlots().size())));
                 caption.set(TranslatableCaption.of("info.plot_list_item"));
                 caption.setTagResolvers(finalResolver.build());
             }

Core/src/main/java/com/plotsquared/core/util/placeholders/PlaceholderRegistry.java

@@ -187,6 +187,7 @@ public final class PlaceholderRegistry {
             }
         });
         this.createPlaceholder("currentplot_biome", (player, plot) -> plot.getBiomeSynchronous().toString());
+        this.createPlaceholder("currentplot_size", (player, plot) -> String.valueOf(plot.getConnectedPlots().size()));
     }
 
     /**