[wpilib][sim] Add Onboard IMU Sim (#8855)

This provides the ability to simulate parts of the Onboard IMU at the
HAL level. This allows team to use and simulate the IMU in code, and a
follow up PR could be made to the halsim_gui to add a new widget to view
and modify the data graphically.

Since the C++ IMU uses radians for angles that is what I did for the
simulator.

Partially deals with #8845

hal/src/main/native/sim/mockdata/IMUData.cpp

@@ -0,0 +1,39 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include "IMUDataInternal.hpp"
+
+using namespace wpi::hal;
+
+namespace wpi::hal {
+namespace init {
+void InitializeIMUData() {
+  static IMUData imu;
+  ::wpi::hal::SimIMUData = &imu;
+}
+}  // namespace init
+
+IMUData* SimIMUData;
+}  // namespace wpi::hal
+
+extern "C" {
+#define DEFINE_CAPI(TYPE, CAPINAME, LOWERNAME)                      \
+  HAL_SIMDATAVALUE_DEFINE_CAPI_NOINDEX(TYPE, HALSIM, IMU##CAPINAME, \
+                                       SimIMUData, LOWERNAME)
+
+DEFINE_CAPI(double, AngleX, angleX)
+DEFINE_CAPI(double, AngleY, angleY)
+DEFINE_CAPI(double, AngleZ, angleZ)
+
+DEFINE_CAPI(double, GyroRateX, gyroRateX)
+DEFINE_CAPI(double, GyroRateY, gyroRateY)
+DEFINE_CAPI(double, GyroRateZ, gyroRateZ)
+
+DEFINE_CAPI(double, AccelX, accelX)
+DEFINE_CAPI(double, AccelY, accelY)
+DEFINE_CAPI(double, AccelZ, accelZ)
+
+DEFINE_CAPI(double, Yaw, yaw)
+
+}  // extern "C"