[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

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

@@ -17,9 +17,7 @@ bool IsTimingPaused();
 
 void StepTiming(uint64_t delta);
 
-uint64_t GetFPGATime();
-
-double GetFPGATimestamp();
+uint64_t GetMonotonicTime();
 
 void SetProgramStarted();
 }  // namespace wpi::hal