SPIGOT-5380, SPIGOT-6958, #772: Add some missing entity API

By: Ollie <69084614+olijeffers0n@users.noreply.github.com>

paper-api/src/main/java/org/bukkit/entity/Parrot.java

@@ -22,6 +22,13 @@ public interface Parrot extends Tameable, Sittable {
      */
     public void setVariant(@NotNull Variant variant);
 
+    /**
+     * Gets whether a parrot is dancing
+     *
+     * @return Whether the parrot is dancing
+     */
+    public boolean isDancing();
+
     /**
      * Represents the variant of a parrot - ie its color.
      */