Add function that can register all the HAL callbacks at once (#646)

Since all of the callbacks issue a string identifier, it makes it
possible and easy to have one function callback, and differentiate the
path to take based on the string.  Hooking up all the callbacks at once
makes it easier for the simulator developer to know when something was
added to wpilib rather than looking at the commits.

hal/src/main/native/include/MockData/DigitalPWMData.h

@@ -38,6 +38,10 @@ void HALSIM_CancelDigitalPWMPinCallback(int32_t index, int32_t uid);
 int32_t HALSIM_GetDigitalPWMPin(int32_t index);
 void HALSIM_SetDigitalPWMPin(int32_t index, int32_t pin);
 
+void HALSIM_RegisterDigitalPWMAllCallbacks(int32_t index,
+                                           HAL_NotifyCallback callback,
+                                           void* param, HAL_Bool initialNotify);
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif