[commands] Add unless() decorator (#4244)

wpilibNewCommands/src/main/java/edu/wpi/first/wpilibj2/command/Command.java

@@ -302,6 +302,18 @@ public interface Command {
     return new ProxyScheduleCommand(this);
   }
 
+  /**
+   * Decorates this command to only run if this condition is not met. If the command is already
+   * running and the condition changes to true, the command will not stop running. The requirements
+   * of this command will be kept for the new conditonal command.
+   *
+   * @param condition the condition that will prevent the command from running
+   * @return the decorated command
+   */
+  default ConditionalCommand unless(BooleanSupplier condition) {
+    return new ConditionalCommand(new InstantCommand(), this, condition);
+  }
+
   /**
    * Schedules this command.
    *