One walk over the geometry a feature holds (3/3, #876) (#1028)

Moves the per-feature geometry handling (transforms, face points, profile selections, point expressions) into one geometry walk in feature_geometry.rs, with a golden record of what each feature kind moves. sheet.perforate holds no world geometry and joins the no-op arm.

crates/doc/src/lib.rs

@@ -19,6 +19,7 @@ mod document;
 mod eval;
 pub mod expr;
 pub mod face_anchor;
+mod feature_geometry;
 mod feature_refs;
 pub use face_anchor::{FaceAnchor, FaceAttachmentStatus};
 pub mod format;