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/clangcodemodel/clangdfindreferences.cpp

@@ -129,7 +129,7 @@ void ClangdFindReferences::Private::handleFindUsagesResult(const QList<Location>
     QObject::connect(search, &SearchResult::canceled, q, [this] {
         canceled = true;
         search->disconnect(q);
-        for (const MessageId &id : qAsConst(pendingAstRequests))
+        for (const MessageId &id : std::as_const(pendingAstRequests))
             client()->cancelRequest(id);
         pendingAstRequests.clear();
         finishSearch();