Untrim: holes removed and a face restored to its natural bounds (#1150)

Adds surface.untrim (#761); the SurfaceUntrim feature is first saved in format 21.

crates/kernel/src/lib.rs

@@ -94,6 +94,7 @@ mod step_in;
 mod step_out;
 mod surface_kind;
 mod surface_offset;
+mod surface_untrim;
 mod surfaces;
 mod sweep_path;
 mod tangent_cylinders;
@@ -137,6 +138,7 @@ pub use step_in::{ImportedBody, StepImport, StepNode, step_cache_alive, step_imp
 pub use step_out::{ExportBody, ExportProduct, StepHeader, step_export_bodies, step_export_products};
 pub use surface_kind::{FaceSurface, face_surface};
 pub use surface_offset::offset_surface;
+pub use surface_untrim::{UntrimHoles, untrim};
 pub use surfaces::{
     copy_faces, extend, extrude_sheet, loft_sheet, patch_edges, patch_region, remove_faces, reverse_faces, revolve_sheet, stitch, sweep_sheet,
     sweep_sheet_points, thicken, trim, unstitch,