[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

wpilibc/src/main/native/include/wpi/simulation/OnboardIMUSim.hpp

@@ -0,0 +1,30 @@
+// 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.
+
+#pragma once
+
+#include "wpi/units/acceleration.hpp"
+#include "wpi/units/angle.hpp"
+#include "wpi/units/angular_velocity.hpp"
+
+namespace wpi::sim {
+
+class OnboardIMUSim {
+ public:
+  void SetAngleX(wpi::units::radian_t angle);
+  void SetAngleY(wpi::units::radian_t angle);
+  void SetAngleZ(wpi::units::radian_t angle);
+
+  void SetGyroRateX(wpi::units::radians_per_second_t rate);
+  void SetGyroRateY(wpi::units::radians_per_second_t rate);
+  void SetGyroRateZ(wpi::units::radians_per_second_t rate);
+
+  void SetAccelX(wpi::units::meters_per_second_squared_t accel);
+  void SetAccelY(wpi::units::meters_per_second_squared_t accel);
+  void SetAccelZ(wpi::units::meters_per_second_squared_t accel);
+
+  void SetYaw(wpi::units::radian_t angle);
+};
+
+}  // namespace wpi::sim