feat(dimension): the standard arrowheads in every arrowhead picker

The dimension style, multileader style and Properties pickers listed
every block of the drawing as an arrowhead, and nothing else. They now
list the 19 standard arrowheads (Closed filled, Open, Dot, Architectural
tick, Oblique, Right angle, Datum triangle, …), followed by any user
arrow block the dimension or style already uses. Picking one creates
its block (`_Open`, `_ArchTick`, …) with the geometry the reference
program writes, so other programs draw the same arrow; ODA reads the
saved file cleanly.

`_Small` now draws as the reference's "Dot small blank", a hollow circle
half the arrow size, instead of a small filled triangle.

Also drops a duplicated "DGN Import" catalog entry left by #1810/#1812.
(#1820, #1821)

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/properties.rs

@@ -554,14 +554,8 @@ impl OpenCADStudio {
             // Arrowheads are blocks; the closed-filled default has no
             // block, so seed the list with it and add the arrowhead
             // blocks (leading underscore) present in the drawing.
-            let arrow_names: Vec<String> = std::iter::once("Closed filled".to_string())
-                .chain(
-                    doc.block_records
-                        .iter()
-                        .filter(|b| b.name.starts_with('_'))
-                        .map(|b| b.name.clone()),
-                )
-                .collect();
+            // Filled in below from the current arrowhead. (#1820)
+            let arrow_names: Vec<String>;
             let block_names: Vec<String> = doc
                 .block_records
                 .iter()
@@ -590,15 +584,11 @@ impl OpenCADStudio {
                         .map(|s| s.name.clone())
                 })
                 .unwrap_or_else(|| "Standard".to_string());
-            let cur_arrow = ml
-                .arrowhead_handle
-                .and_then(|h| {
-                    doc.block_records
-                        .iter()
-                        .find(|b| b.handle == h)
-                        .map(|b| b.name.clone())
-                })
-                .unwrap_or_else(|| "Closed filled".to_string());
+            let cur_arrow = crate::entities::arrowheads::label(
+                doc,
+                ml.arrowhead_handle.unwrap_or(codec::Handle::NULL),
+            );
+            arrow_names = crate::entities::arrowheads::options([cur_arrow.as_str()]);
             let cur_ltype = ml
                 .line_type_handle
                 .and_then(|h| {