[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/test/native/cpp/simulation/SimDeviceSimTest.cpp

@@ -0,0 +1,36 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019-2020 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/SimDevice.h>
+#include <wpi/StringRef.h>
+
+#include "frc/simulation/SimDeviceSim.h"
+#include "gtest/gtest.h"
+
+using namespace frc::sim;
+
+TEST(SimDeviceSimTests, TestBasic) {
+  hal::SimDevice dev{"test"};
+  hal::SimBoolean devBool = dev.CreateBoolean("bool", false, false);
+
+  SimDeviceSim sim{"test"};
+  hal::SimBoolean simBool = sim.GetBoolean("bool");
+  EXPECT_FALSE(simBool.Get());
+  simBool.Set(true);
+  EXPECT_TRUE(devBool.Get());
+}
+
+TEST(SimDeviceSimTests, TestEnumerateDevices) {
+  hal::SimDevice dev{"test"};
+
+  bool foundit = false;
+  SimDeviceSim::EnumerateDevices(
+      "te", [&](const char* name, HAL_SimDeviceHandle handle) {
+        if (wpi::StringRef(name) == "test") foundit = true;
+      });
+  EXPECT_TRUE(foundit);
+}