Generate heal location constants automatically

[GriffinRichards]

• Generates include/constants/heal_locations.h using the heal location data, so users don't need to manage them at all.
• Reverses course a bit from Move heal locations data to their associated map.json #673 by moving heal location data from the respective map.json files back to a single separate file. There was a few reasons for this:
  • Getting the correct value order for heal location constants would otherwise be much messier, probably requiring something like connection_include_order.
  • After Generate local IDs from map.json files #675 the value for respawn_npc can be updated automatically, so it's less important to have that in map.json.
  • It should be faster. Editing heal location data will no longer require processing every map.json file.
  • The inja template should be much simpler to understand at a glance than the C++ code that was in mapjson.