Convert map JSON data to C instead of asm

[GriffinRichards]

Putting this here so I don't forget (or in case someone else takes an interest):

At the moment, the data in data/maps.s and data/map_events.s is assembly data that gets written by mapjson using the JSON data for maps/layouts. This is facilitated with some assembly macros in asm/macros/map.inc, which users then need to keep in sync with their corresponding structs in C if they make any changes to them. It would require less management from users if mapjson (or jsonproc) would convert the JSON data to C instead.

The same should also be done for data/tilesets.s at some point, but this data is currently read/written by Porymap directly rather than as JSON data, so this would be a breaking change.

EDIT: The latter point has been handled by #1796