Rain penetrates S1MAPI buildings and NPCs use umbrellas indoors

[hdlmrell]

Rain falls through S1MAPI-built structures. The game's weather system appears to use terrainData for rain placement, which doesn't account for custom buildings. As a result:

• Rain visually falls inside buildings
• NPCs indoors detect rain and switch to umbrella/running behavior

[hdlmrell]

I have this fixed for my consumer mod, no further research is necessary at this time. I will work on the PR when I can.

[hdlmrell]

Implementation here:

hdlmrell/OTC-S1-Mod@89c0b04#diff-6b6ef3b4f8a6ae3665f1eabd18afd8661d663e13c7220585c1d0ecacd1fd6b31R16-R153