[hal] Implement stub mockdata on RoboRIO (#2575)

This makes it much more user-friendly to use simulation classes without needing
to ifdef for C++ to avoid linker errors or be very careful about construction
to avoid runtime errors in Java.

hal/src/main/native/athena/mockdata/EncoderData.cpp

@@ -0,0 +1,47 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2017-2020 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "hal/simulation/EncoderData.h"
+
+#include "hal/simulation/SimDataValue.h"
+
+extern "C" {
+int32_t HALSIM_FindEncoderForChannel(int32_t channel) { return 0; }
+
+void HALSIM_ResetEncoderData(int32_t index) {}
+
+int32_t HALSIM_GetEncoderDigitalChannelA(int32_t index) { return 0; }
+
+int32_t HALSIM_GetEncoderDigitalChannelB(int32_t index) { return 0; }
+
+HAL_SimDeviceHandle HALSIM_GetEncoderSimDevice(int32_t index) { return 0; }
+
+#define DEFINE_CAPI(TYPE, CAPINAME, RETURN) \
+  HAL_SIMDATAVALUE_STUB_CAPI(TYPE, HALSIM, Encoder##CAPINAME, RETURN)
+
+DEFINE_CAPI(HAL_Bool, Initialized, false)
+DEFINE_CAPI(int32_t, Count, 0)
+DEFINE_CAPI(double, Period, 0)
+DEFINE_CAPI(HAL_Bool, Reset, false)
+DEFINE_CAPI(double, MaxPeriod, 0)
+DEFINE_CAPI(HAL_Bool, Direction, false)
+DEFINE_CAPI(HAL_Bool, ReverseDirection, false)
+DEFINE_CAPI(int32_t, SamplesToAverage, 0)
+DEFINE_CAPI(double, DistancePerPulse, 0)
+
+void HALSIM_SetEncoderDistance(int32_t index, double distance) {}
+
+double HALSIM_GetEncoderDistance(int32_t index) { return 0; }
+
+void HALSIM_SetEncoderRate(int32_t index, double rate) {}
+
+double HALSIM_GetEncoderRate(int32_t index) { return 0; }
+
+void HALSIM_RegisterEncoderAllCallbacks(int32_t index,
+                                        HAL_NotifyCallback callback,
+                                        void* param, HAL_Bool initialNotify) {}
+}  // extern "C"