[hal] Consistently use .hpp for C++ header content

Some headers were renamed, but others were split.

hal/src/main/native/sim/MockHooksInternal.hpp

@@ -0,0 +1,25 @@
+// 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 <stdint.h>
+
+namespace wpi::hal {
+void RestartTiming();
+
+void PauseTiming();
+
+void ResumeTiming();
+
+bool IsTimingPaused();
+
+void StepTiming(uint64_t delta);
+
+uint64_t GetFPGATime();
+
+double GetFPGATimestamp();
+
+void SetProgramStarted();
+}  // namespace wpi::hal