Tracking Porymap breaking changes

This issue is for tracking a few potential improvements that haven't been made because they would require changes to Porymap. This way if it's decided one breaking change should be made the rest can be easily referred to and piled on.

[x] object_event_graphics_info.h could be made more readable and less prone to errors from missing a field by using designated initializers (see #1413). Porymap is currently unable to parse this.
[x] As of #1550 files in graphics/pokenav are organized into subfolders, except for those read/written by Porymap whose paths would need to be updated. See #1636
[x] #1558 adds among other things constants for special warp ids. They can't be used in the dest_warp_id field because Porymap treats this as an int and won't properly handle macro names. See #1755
[x] Additional constants in include/constants/heal_locations.h aren't preserved by Porymap, which prevents adding HEAL_LOCATION_NONE. See #1671
[x] Not sure how worth changing it is, but the only reason data/tilesets.s is still in assembly is because Porymap expects it to be. Related: #1736
[x] MAP_NONE is more accurately MAP_DYNAMIC, and MAP_UNDEFINED would be MAP_NONE. This could be updated, but Porymap currently hard codes "MAP_NONE" as "None" and expects any other MAP_ constant in a warp destination field to be a valid map, or it rejects the event. See #1755

pret / pokeemerald

Tracking Porymap breaking changes #1554