Sheet metal: the flat-pattern DXF writes ellipses and splines exactly (#1096)

sheet.export_dxf writes an AutoCAD 2000 drawing with ELLIPSE and SPLINE entities for ellipses, splines and text outlines instead of chords, with curves: arcs for machines that read only lines and arcs. Perforation circles go through the same writer. Closes #1089.

crates/io/src/lib.rs

@@ -10,6 +10,7 @@ pub mod catalog;
 mod design;
 mod design_metadata;
 mod dxf;
+mod dxf_out;
 pub use design::{
     DesignCompression, DesignContainerReader, DesignGeometry, DesignPreview, THUMBNAIL_SIZE, is_design_container, read_design_file,
     read_design_geometry, read_design_preview, read_design_thumbnail, read_design_thumbnail_file, write_design_container,
@@ -25,6 +26,7 @@ pub mod urdf;
 pub mod vfs;
 
 pub use dxf::{read_dxf, write_dxf};
+pub use dxf_out::{DxfEntity, DxfLayer, DxfShape, loop_shapes, seg_shape, write_dxf_drawing};
 pub use legacy_dir::{APP_ID, LEGACY_APP_ID, adopt_legacy_dir, legacy_flatpak_path};
 pub use safe_write::{backup_path, write_atomic};
 pub use sketch2d::{Geom2, MAX_DRAWING_BYTES};