[sim] Move Sim classes from HAL to wpilibc/j (#2549)

Also move some things in HAL for consistency.

WAS:
C++:
- C APIs: #include "mockdata/AccelerometerData.h"
- User side class: #include "simulation/AccelerometerSim.h"
Java:
- JNI APIs: hal.sim.mockdata.AccelerometerData (and a few classes in hal.sim)
- User side classes: hal.sim.AccelerometerSim

IS:
C++:
- C APIs: #include "hal/simulation/AccelerometerData.h"
- C++ class: #include "frc/simulation/AccelerometerSim.h"
Java:
- JNI APIs: hal.simulation.AccelerometerData
- User side class: wpilibj.simulation.AccelerometerSim

wpilibc/src/main/native/include/frc/simulation/SimHooks.h

@@ -0,0 +1,34 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2018-2020 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <hal/simulation/MockHooks.h>
+
+namespace frc {
+namespace sim {
+
+void SetRuntimeType(HAL_RuntimeType type) { HALSIM_SetRuntimeType(type); }
+
+void WaitForProgramStart() { HALSIM_WaitForProgramStart(); }
+
+void SetProgramStarted() { HALSIM_SetProgramStarted(); }
+
+bool GetProgramStarted() { return HALSIM_GetProgramStarted(); }
+
+void RestartTiming() { HALSIM_RestartTiming(); }
+
+void PauseTiming() { HALSIM_PauseTiming(); }
+
+void ResumeTiming() { HALSIM_ResumeTiming(); }
+
+bool IsTimingPaused() { return HALSIM_IsTimingPaused(); }
+
+void StepTiming(uint64_t delta) { HALSIM_StepTiming(delta); }
+
+}  // namespace sim
+}  // namespace frc