All typedefs for structs that were present in other header
files have been moved to here. (Except node_t because the
renderer and netcode both define node_t LOL.)
Events have a player ID instead of adding billions of keys for separate gamepads. Axis movement (mouse movement, analog sticks) now are counted as keys, so axes don't need to be separately implemented for all controls. Game controls emulate a Saturn controller (some of the external functions like screenshot / gif should be readded, but I got lazy)
This will allow later us to save a config for a controller that can be reused for any player slot, which is one of the main goals for profiles.
Only just enough was made to use the new input system to make it compile. Menus in this branch should aim to move to using PlayerInputDown entirely, instead of using hardcoded keys & simply remapping to those
