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_background_widget.cpp

@@ -12,6 +12,7 @@
 #include <QPaintEvent>
 #include <QPainter>
 #include <QDebug>
+#include <QFile>
 
 #ifdef Q_OS_WIN
 #include <QtPlatformHeaders/qwindowswindowfunctions.h>