[commands] Add missing PS4 triangle methods (#4576)

wpilibNewCommands/src/main/java/edu/wpi/first/wpilibj2/command/button/CommandPS4Controller.java

@@ -205,6 +205,27 @@ public class CommandPS4Controller extends CommandGenericHID {
     return m_hid.cross(loop).castTo(Trigger::new);
   }
 
+  /**
+   * Constructs an event instance around the triangle button's digital signal.
+   *
+   * @return an event instance representing the triangle button's digital signal attached to the
+   *     {@link CommandScheduler#getDefaultButtonLoop() default scheduler button loop}.
+   */
+  public Trigger triangle() {
+    return triangle(CommandScheduler.getInstance().getDefaultButtonLoop());
+  }
+
+  /**
+   * Constructs an event instance around the triangle button's digital signal.
+   *
+   * @param loop the event loop instance to attach the event to.
+   * @return an event instance representing the triangle button's digital signal attached to the
+   *     given loop.
+   */
+  public Trigger triangle(EventLoop loop) {
+    return m_hid.triangle(loop).castTo(Trigger::new);
+  }
+
   /**
    * Constructs an event instance around the circle button's digital signal.
    *