Models and decals (and a bunch of other things as a side-effect) kept pointers to the simulation and called terrain/water to get data. Following D3552, we can replace all those with more appropriate graphics/ call.

This is intended to be part of the greater plan™ to thread the simulation from the rendering, though that's still a fair ways off.

It also incorporates a fix for floating decals, who had incorrectly calculated bounds.

Run the game and check that things still work properly.