feat: add methods to add and remove viewers to Waypoint

Author: Privatech38

api/src/main/java/net/kyori/adventure/waypoint/Waypoint.java

@@ -208,6 +208,32 @@ static VectorWaypoint vector(final Key style, final TextColor color, final int x
   @UnmodifiableView
   Iterable<? extends Audience> viewers();
 
+  /**
+   * Track this waypoint for {@code viewer}.
+   *
+   * @param viewer the viewer
+   * @return the waypoint
+   * @see Audience#trackWaypoint(Waypoint)
+   * @since 5.1.0
+   */
+  default Waypoint addViewer(final Audience viewer) {
+    viewer.trackWaypoint(this);
+    return this;
+  }
+
+  /**
+   * Untrack this waypoint for {@code viewer}.
+   *
+   * @param viewer the viewer
+   * @return the waypoint
+   * @see Audience#untrackWaypoint(Waypoint)
+   * @since 5.1.0
+   */
+  default Waypoint removeViewer(final Audience viewer) {
+    viewer.untrackWaypoint(this);
+    return this;
+  }
+
   /**
    * A listener for changes on a {@link Waypoint}.
    *