Xref attach: Attach dialog, reference prompts, and xref drawings other applications can open

Attach External Reference dialog after XATTACH / ATTACH; ATTACH routes
drawings, PDFs and images; placement prompts and messages follow the
reference (presets, Corner/XYZ, nonzero check, existing definition reuse,
missing file, self-reference); name keeps the file's case; overlay and
path type at attach; one undo step for definition and INSERT; -XREF option
prompt and `?` table; XREF opens the palette; ER alias; xref Properties
rows; dependent symbols flagged and remapped and resolved content left out
of the saved file; dialog_ok automation action; localized labels.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ui/window/block_definition.rs

@@ -155,7 +155,7 @@ impl BlockDefinitionState {
     }
 }
 
-fn group<'a>(
+pub(crate) fn group<'a>(
     title: impl Into<String>,
     body: impl Into<Element<'a, Message>>,
     height: impl Into<Length>,
@@ -185,7 +185,7 @@ fn group<'a>(
     .into()
 }
 
-fn labeled_checkbox<'a>(
+pub(crate) fn labeled_checkbox<'a>(
     label: impl Into<String>,
     is_checked: bool,
     on_toggle: impl Fn(bool) -> Message + 'a,