Fix Qt6 API compatibility in LtsWidgets

- lts_date_time_edit_p.cpp: Replace QWheelEvent::delta() with angleDelta().y()
- lts_notification_box.cpp: Remove QStyleOption::init() call (removed in Qt6)
- lts_text_editor2.cpp: Remove QTextCodec include, use QString::fromUtf8 instead

All changes are Qt6 API compatibility fixes required for building with Qt 6.10.2.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

qt6-after/qt6-migrated-legatus/Lts/Common/LtsWidgets/lts_text_editor2.cpp

@@ -21,7 +21,6 @@
 #include <QFontDatabase>
 #include <QMenu>
 #include <QMenuBar>
-#include <QTextCodec>
 #include <QTextEdit>
 #include <QStatusBar>
 #include <QToolBar>
@@ -439,8 +438,7 @@ bool LtsTextEditor2::load(const QString &f)
     return false;
 
   QByteArray data = file.readAll();
-  QTextCodec *codec = Qt::codecForHtml(data);
-  QString str = codec->toUnicode(data);
+  QString str = QString::fromUtf8(data);
   if (Qt::mightBeRichText(str)) {
     QUrl baseUrl = (f.front() == QLatin1Char(':') ? QUrl(f) : QUrl::fromLocalFile(f)).adjusted(QUrl::RemoveFilename);
     m_textEdit->document()->setBaseUrl(baseUrl);