LtsWidgets: Qt6 API fixes complete

- QComboBox::activated signal: QString→int parameter (lts_text_editor)
- qAsConst→std::as_const (5 files)
- localPos()→position() (lts_height_plot_widget)
- setMargin→setContentsMargins (tests/window.cpp)
- CMAKE_AUTOUIC OFF + include in header for MOC
- enterEvent(QEnterEvent*) signature fixes
- QRegExp→QRegularExpression replacements

All LtsWidgets module files now Qt6-compatible.

qt6-after/qt6-migrated-legatus/Lts/Common/LtsWidgets/lts_date_time_edit.cpp

@@ -80,7 +80,7 @@ public:
   void setupUi(QWidget *parent)
   {
     gridLayout = new QGridLayout(parent);
-    gridLayout->setMargin(0);
+    gridLayout->setContentsMargins(0, 0, 0, 0);
 
     int iStart = 3; // 3 invisible widgets before
 
@@ -1420,7 +1420,7 @@ void LtsDateTimeEdit::onCheckBoxChanged()
   }
 
   bEnable = checkBox()->isChecked();
-  for (auto w : qAsConst(widgets))
+  for (auto w : std::as_const(widgets))
   {
     if (w)
       w->setEnabled(bEnable);