Add base game new region settings JSON

[ShnitzelX2]

Summary

None

Purpose of change

• From [WIP] Region settings overhaul #82631

Describe the solution

See title; the base settings have to be merged before mod settings are merged.

This PR pulls from commit 237224e to avoid a loading failure. building_bin::unfinalized_buildings is unused for region_settings_new, so it would be empty when loading and cause an error.

This PR also pulls from commit 09d8219 to move the region settings file deeper so that objects it uses are loaded first.

Describe alternatives you've considered

Testing

Loaded game without error, worked in #82631. CI should be fine, but double-check

Additional context

[GuardianDll]

Mods-([slow] ~starting_items)=> ../tests/overmap_test.cpp:521: FAILED:
Mods-([slow] ~starting_items)=> explicitly with messages:
Mods-([slow] ~starting_items)=>   id := int_id( "hw_reserved" )
Mods-([slow] ~starting_items)=>   oter_type_id was found in map but had SHOULD_NOT_SPAWN flag

[ShnitzelX2]

This test failure is older, from the highways PR, and I still can't figure out why it's happening. I haven't seen a single instance of reserved OMTs in-game, so it may be test-only.