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 <[email protected]>

src/command.rs

@@ -2838,9 +2838,9 @@ pub trait CadCommand: Send {
         false
     }
 
-    /// If this command is XATTACH, returns the file path to attach.
-    /// Default: None.
-    fn xattach_path(&self) -> Option<String> {
+    /// If this command is XATTACH, what it attaches and how the reference is
+    /// stored. Default: None.
+    fn xattach_request(&self) -> Option<crate::modules::insert::xattach::XrefAttachRequest> {
         None
     }