Loft: refuse a section with a hole instead of filling it (#1184) (#1254)

A loft section with a hole is refused with a clear message instead of being lofted as if filled, in both section-to-section and section-to-point lofts. Fixes #1184.

crates/engine/src/tests.rs

@@ -308,6 +308,7 @@ mod boolean_diagnostics;
 mod component_frames;
 mod large_step_import;
 mod loft_cut;
+mod loft_ring;
 mod loft_spacing;
 mod mirror_planes;
 mod path_scope;