PDFSHXTEXT: recognise SHX text geometry as MText

Adds PDFSHXTEXT with the PDF Text Recognition Settings dialog, its
command-line form, the PDFSHXLAYER / PDFSHXBESTFONT / PDFSHXTEXTSETTINGS
variables and the profile settings they are kept in.

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

src/app/commands/mod.rs

@@ -22,6 +22,7 @@ mod pc_colormap;
 mod pc_extract;
 mod pdf_dialogs;
 pub(crate) mod pdf_import;
+mod pdf_shx_text;
 mod pdf_underlay;
 mod plotvars;
 mod point_cloud;
@@ -775,6 +776,9 @@ inventory::submit!(crate::command::CommandRegistration {
         "PDFIMPORTFILTER",
         "PDFIMPORTLAYERS",
         "PDFIMPORTIMAGEPATH",
+        "PDFSHXLAYER",
+        "PDFSHXBESTFONT",
+        "PDFSHXTEXTSETTINGS",
         "XDWGFADECTL",
         "POINTCLOUDCLIPFRAME",
         "POINTCLOUDDENSITY",