Fix Instancer working w/ vertex spacing

[TokisanGames]

Fixes #479

To test at spacing <1, 1, >1

• painting, w/ slope and ALT slope
• erasing, w/slope and ALT slope
• Saving & reloading
• Removing regions where instances were created at all scales to ensure the instances are attached to the proper region
• Sculpting underneath instances

Key reminder: ALT to inverse slope. CTRL+SHIFT to remove all instances.

The only thing I've seen is if you remove a region when vertex_spacing != 0, the instances in an adjacent region transform slightly. They aren't removed nor moved, but they seem to grow, shrink, or shear slightly. It isn't noticable at vertex_spacing 1. It may be due to the way we're scaling the MMI laterally only.

Remaining issues from first commit:

• update_transforms < 1 doesn't work
• Vertex spacing transforms the MMI!! And working on fixing this broke everything else.