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_text_editor.h

@@ -46,9 +46,9 @@ private slots:
   void slotClipboardDataChanged();
   void slotTextColor();
   void slotBackgroundColor();
-  void slotTextSize(const QString &p);
+  void slotTextSize(int index);
   void slotTextSizeEditingFinished();
-  void slotTextFamily(const QString &f);
+  void slotTextFamily(int index);
   void slotTextItalic();
   void slotTextUnderline();
   void slotTextBold();