Surface Loft: sheets through open or closed sections (#847)

Surface Loft lofts open or closed curve chains, one section per sketch in pick order, into surface bodies. Adds the SurfaceLoft feature (format 18 note), the surface.loft command, a dialog with Edit Feature support, and kernel and engine tests.

Part of #757.

crates/doc/src/params.rs

@@ -290,6 +290,7 @@ impl FeatureKind {
             | FeatureKind::Loft { .. }
             | FeatureKind::Sweep { .. }
             | FeatureKind::SurfaceSweep { .. }
+            | FeatureKind::SurfaceLoft { .. }
             | FeatureKind::Import { .. }
             | FeatureKind::MeshImport { .. }
             | FeatureKind::BodyTransfer { .. } => {}