Extend any surface: natural, tangent and curvature, up to a target (#760) (#1166)

Extend works on any surface: natural (continuing the face's own surface), tangent (G1 run-off) or curvature (G2 run-off), by a distance, up to a plane or face, or back to the surface's bounds, with neighbouring edges lengthened to meet. Untrim and Extend share face parameter-loop helpers. The new SurfaceExtend fields are noted under format 21. Closes #760.

crates/kernel/src/lib.rs

@@ -28,6 +28,7 @@ mod coplanar;
 mod curveblend;
 mod delete_face;
 mod emboss;
+mod face_params;
 #[cfg(test)]
 mod face_source_tests;
 mod fill;
@@ -92,6 +93,7 @@ mod splitface;
 mod step;
 mod step_in;
 mod step_out;
+mod surface_extend;
 mod surface_kind;
 mod surface_offset;
 mod surface_ruled;
@@ -137,6 +139,7 @@ pub use splitface::{SplitTool, split_body, split_faces, split_faces_with_map};
 pub use step::step_export;
 pub use step_in::{ImportedBody, StepImport, StepNode, step_cache_alive, step_import, step_import_shared, step_orientation_errors, step_validate};
 pub use step_out::{ExportBody, ExportProduct, StepHeader, step_export_bodies, step_export_products};
+pub use surface_extend::{ExtendLimit, ExtendMode, ExtendOptions, extend_surface};
 pub use surface_kind::{FaceSurface, face_surface};
 pub use surface_offset::offset_surface;
 pub use surface_ruled::{Ruled, RuledCorners, RuledMode, ruled_surface};