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 <noreply@anthropic.com>

src/entities/dimension.rs

@@ -1953,15 +1953,6 @@ pub fn style_sections(
         }
     };
 
-    let mut arrow_options: Vec<String> = std::iter::once("Closed filled".to_string())
-        .chain(
-            document
-                .block_records
-                .iter()
-                .map(|record| record.name.clone())
-                .filter(|name| !name.is_empty()),
-        )
-        .collect();
     let mut linetype_options: Vec<String> = document
         .line_types
         .iter()
@@ -2001,11 +1992,9 @@ pub fn style_sections(
     } else {
         arrow_name(ov::DIMBLK2, s.dimblk2, &s.dimblk2_name)
     };
-    for current in [&arrow_1, &arrow_2] {
-        if !arrow_options.contains(current) {
-            arrow_options.push(current.clone());
-        }
-    }
+    // The standard arrowheads, then any user arrow block in use. (#1820)
+    let arrow_options =
+        crate::entities::arrowheads::options([&arrow_1, &arrow_2].map(String::as_str));
     for current in [
         linetype(ov::DIMLTYPE, s.dimltex_handle),
         linetype(ov::DIMLTEX1, s.dimltex1_handle),
@@ -3402,16 +3391,13 @@ fn choice_value(selected: &str, options: &[&str]) -> crate::scene::model::object
     }
 }
 
+/// The arrowhead picker's name for `handle`; `fallback` names a block the
+/// drawing does not hold.
 fn block_name(document: &CadDocument, handle: codec::Handle, fallback: &str) -> String {
-    if handle.is_null() {
-        return "Closed filled".to_string();
+    if !handle.is_null() && !document.block_records.iter().any(|b| b.handle == handle) {
+        return crate::entities::arrowheads::label_for_block(fallback);
     }
-    document
-        .block_records
-        .iter()
-        .find(|record| record.handle == handle)
-        .map(|record| record.name.clone())
-        .unwrap_or_else(|| fallback.to_string())
+    crate::entities::arrowheads::label(document, handle)
 }
 
 fn linetype_name(document: &CadDocument, handle: codec::Handle) -> String {