[sim] Provide method to set the runtime type (#2539)

This is needed for extensions that effectively access real hardware and
want to disable the "simulation" parts of user code.

hal/src/main/native/sim/jni/SimulatorJNI.cpp

@@ -108,6 +108,18 @@ jmethodID GetSpiReadAutoReceiveBufferCallback() {
 }  // namespace hal
 
 extern "C" {
+/*
+ * Class:     edu_wpi_first_hal_sim_mockdata_SimulatorJNI
+ * Method:    setRuntimeType
+ * Signature: (I)V
+ */
+JNIEXPORT void JNICALL
+Java_edu_wpi_first_hal_sim_mockdata_SimulatorJNI_setRuntimeType
+  (JNIEnv*, jclass, jint type)
+{
+  HALSIM_SetRuntimeType(static_cast<HAL_RuntimeType>(type));
+}
+
 /*
  * Class:     edu_wpi_first_hal_sim_mockdata_SimulatorJNI
  * Method:    waitForProgramStart