Cleanup forward declarations, unnecessary returns, duplicate function
declarations and replace literals with constants/enum variants where
applicable.
Rename struct members based on `overlay005/scrcmd_move_tutor`, some
simple functions, and give a temporary name to the struct.
- `resultVar` -> `destVarID`
- Clean up member names for `HiddenLocation` and `DistributionEvent`
- `Set/Clear` -> `Enable/Disable` for HiddenLocation script macros
- `ScrCmd_SetOrClearHiddenLocation` -> `ScrCmd_SetHiddenLocation`
- `SYSTEM_VARS_BLOCK_SIZE` -> `NUM_SYSTEM_VARS`
- Identify `scripts_unk_0412` -> `scripts_init_new_game`
- Add `SCRIPT_ID_OFFSET_INIT_NEW_GAME` constant definition
- Add `SCRIPT_ID` functional macro
- Use `SCRIPT_ID(INIT_NEW_GAME, 0)` in `FieldSystem_InitNewGameState`
- Promote `LCRNG_MULTIPLIER` in `math.c` from private to public
- Use private `LCRNG_INCREMENT` in `system_vars.c` for lottery sync
