[hal,wpilib] Rename FPGA clock to monotonic clock (#8672)

- Remove status return from HAL level (clock getting should never fail)
- Remove 32-bit timestamp expand function
- Make monotonic_clock.hpp (formerly fpga_clock.hpp) header-only and
move to root hal include directory

wpilibc/src/main/native/include/wpi/hardware/motor/MotorSafety.hpp

@@ -114,7 +114,7 @@ class MotorSafety {
   bool m_enabled = false;
 
   // The FPGA clock value when the motor has expired
-  wpi::units::second_t m_stopTime = Timer::GetFPGATimestamp();
+  wpi::units::second_t m_stopTime = Timer::GetMonotonicTimestamp();
 
   mutable wpi::util::mutex m_thisMutex;
 };