Levels compatibility
Add levels measurement function
- When over a levels tile, default to the bottom elevation of that tile.
- When over a levels hole, default to the bottom elevation of that hole.
- When starting at a token, stay at the floor level for that token unless over a hole or other token.
- Optional label for the current floor level.
Switch to using canvas.terrain.terrainsFromPixels
(requires Enhanced Terrain Layer 1.0.30+).