* Remove fix16.h/cpp and utilise library from m_fixed.h.
* Extend m_fixed.h with two inline functions for int to/from float operations.
* Replace fix16_floor operations with those from xs_Float.h
* Replace multiple Q16.16 conversions from 0 to just be 0.
* Replaced all found in-game bit-shifts and multiplications/divisions with inline functions from m_fixed.h
* Replaced many casts of FRACUNIT as double in SW's panel.cpp as it is converted to double by way of type promotion.
* Fixed missed precision fixes in SW's panel.cpp where some types weren't declared correctly.
* Replaced 100+ `Cos()/Sin() >> 16` operations for Blood with inline functions `CosScale16()/SinScale16()`.
This timer only gets incremented by the main game ticker when the playsim is running.
This timer gets used for all playsim-related timing and animations so that these are decoupled from imprecisions in the global timer.
* Build timer still requires initialisation due to multiple `timerSetCallback()` that still need to work.
# Conflicts:
# source/core/menu/menu.cpp
# source/games/duke/src/game.cpp
