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/ui/window/mod.rs

@@ -27,6 +27,7 @@ pub mod open_progress;
 pub mod options;
 pub mod pc_manager;
 pub mod pdf_dialogs;
+pub mod pdf_shx_dialog;
 pub mod plot;
 pub mod plugin_manager;
 pub mod print_all;