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

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

hal/src/main/native/cpp/jni/HAL.cpp

@@ -151,6 +151,21 @@ Java_edu_wpi_first_hal_HAL_getRSLState
   return val;
 }
 
+/*
+ * Class:     edu_wpi_first_hal_HAL
+ * Method:    getSystemTimeValid
+ * Signature: ()Z
+ */
+JNIEXPORT jboolean JNICALL
+Java_edu_wpi_first_hal_HAL_getSystemTimeValid
+  (JNIEnv* env, jclass)
+{
+  int32_t status = 0;
+  bool val = HAL_GetSystemTimeValid(&status);
+  CheckStatus(env, status);
+  return val;
+}
+
 /*
  * Class:     edu_wpi_first_hal_HAL
  * Method:    getPortWithModule