Port from qAsConst() to std::as_const()

We've been requiring C++17 since Qt 6.0, and our qAsConst use finally
starts to bother us (QTBUG-99313), so time to port away from it
now.

Since qAsConst has exactly the same semantics as std::as_const (down
to rvalue treatment, constexpr'ness and noexcept'ness), there's really
nothing more to it than a global search-and-replace.

Task-number: QTBUG-99313
Change-Id: I88edd91395849574436299b8badda21bb93bea39
Reviewed-by: hjk <hjk@qt.io>

src/plugins/coreplugin/themechooser.cpp

@@ -179,7 +179,7 @@ static void addThemesFromPath(const QString &path, QList<ThemeEntry> *themes)
     themeDir.setNameFilters({extension});
     themeDir.setFilter(QDir::Files);
     const QStringList themeList = themeDir.entryList();
-    for (const QString &fileName : qAsConst(themeList)) {
+    for (const QString &fileName : std::as_const(themeList)) {
         QString id = QFileInfo(fileName).completeBaseName();
         themes->append(ThemeEntry(Id::fromString(id), themeDir.absoluteFilePath(fileName)));
     }