Remove bitmap_byte_length member from zint_symbol

(was only set on BMP output to length of BMP pixel array)
EXCODE39: change to display check digit in HRT by default
CODE39/EXCODE39/LOGMARS: new hidden check digit option
  (`option_2 = 2`)
qr.c: suppress bogus gcc-13 warning (only appears on optimize)
GUI: move some symbology-specific options into Data Tab so
  separate tab unnecessary (those with few options and no
  Composite/ECI), namely: all C25XXX, CODE39/EXCODE39/LOGMARS,
  MSI_PLESSEY, CODABAR, DAFT, DPD, MAILMARK_2D, ITF-14, PZN,
  UPNQR, CHANNEL, CODE93 and VIN, adjusting grp uis.
  change Data dialog button (ellipsis) QToolButton -> QPushButton
  & vice versa zap/clear/eye/swap/scale buttons QPushButton ->
  QToolButton for better mac compat (also makes sense);
  remove some mac hacks that no longer seem necessary;
  use folder icon for Export dialog directory button
manual: document new Symbology-specific groupbox & CODE39/etc
  hidden check digit option; add annexes on Qt and Tcl backends;
  narrow some tables for better txt output;
  remove echoed image tags in txt (pandoc 3.1.5 regression?);
  add one-page HTML output to Makefile; also tex output (debug);
  add class attributes to images to aid HTML styling;
  various other fiddlings

frontend_qt/extData.ui

@@ -20,7 +20,7 @@
   <property name="modal">
    <bool>true</bool>
   </property>
-  <layout class="QVBoxLayout" name="verticalLayout">
+  <layout class="QVBoxLayout" name="vLayoutData">
    <item>
     <widget class="QLabel" name="label">
      <property name="text">
@@ -45,7 +45,7 @@
     </widget>
    </item>
    <item>
-    <layout class="QHBoxLayout" name="horizontalLayout">
+    <layout class="QHBoxLayout" name="hLayoutData">
      <property name="sizeConstraint">
       <enum>QLayout::SetDefaultConstraint</enum>
      </property>