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_message_dialog.cpp

@@ -81,7 +81,7 @@ LtsMessageDialogNew::LtsMessageDialogNew(QWidget *parent, const QString &message
   mainLayout->addWidget(messageLabel);
 
   QHBoxLayout *buttonLayout = new QHBoxLayout;
-  buttonLayout->setMargin(0);
+  buttonLayout->setContentsMargins(0, 0, 0, 0);
 
   // TODO: FIXME: can this be called after the selection was made and the shadow just dies ?
   //connect(m_dialog, &LtsFramelessDialog::rejected, this, &LtsMessageDialogHelper::slotCancel); // respect that non-modal dialogs can be closed by clicking outside of it