[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

simulation/halsim_gui/src/main/native/cpp/Field2D.cpp

@@ -14,8 +14,8 @@
 #include <imgui.h>
 
 #define IMGUI_DEFINE_MATH_OPERATORS
+#include <hal/simulation/SimDeviceData.h>
 #include <imgui_internal.h>
-#include <mockdata/SimDeviceData.h>
 #include <units/units.h>
 #include <wpi/Path.h>
 #include <wpi/SmallString.h>