[cmd3] Add rising and falling edge trigger factories (#8366)

`Trigger.getAsBoolean()` behavior has been changed from passing through
the underlying boolean supplier to returning the latest cached signal as
determined by the most recent call to `poll()`. This allows rising and
falling edge triggers to have a consistent return value over an entire
polling cycle, rather than only being high for the _first_ check in a
cycle.

Closes #8309

wpilibj/src/main/java/org/wpilib/event/EventLoop.java

@@ -30,6 +30,19 @@ public final class EventLoop {
     m_bindings.add(action);
   }
 
+  /**
+   * Unbind an action from running when the loop is polled. Has no effect if the given action is not
+   * already bound.
+   *
+   * @param action the action to unbind.
+   */
+  public void unbind(Runnable action) {
+    if (m_running) {
+      throw new ConcurrentModificationException("Cannot unbind EventLoop while it is running");
+    }
+    m_bindings.remove(action);
+  }
+
   /** Poll all bindings. */
   @SuppressWarnings("PMD.UnusedAssignment")
   public void poll() {