[wpilib] RobotController: Add isSystemTimeValid() (#5696)

This returns true when the system date/time (wall clock) is valid.

wpilibj/src/main/java/edu/wpi/first/wpilibj/RobotController.java

@@ -121,6 +121,15 @@ public final class RobotController {
     return HAL.getRSLState();
   }
 
+  /**
+   * Gets if the system time is valid.
+   *
+   * @return True if the system time is valid, false otherwise
+   */
+  public static boolean isSystemTimeValid() {
+    return HAL.getSystemTimeValid();
+  }
+
   /**
    * Get the input voltage to the robot controller.
    *