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/texteditor/codeassist/genericproposalmodel.cpp

@@ -283,7 +283,7 @@ void GenericProposalModel::filter(const QString &prefix)
     m_currentItems.clear();
     const QString lowerPrefix = prefix.toLower();
     const bool checkInfix = prefix.size() >= 3;
-    for (const auto &item : qAsConst(m_originalItems)) {
+    for (const auto &item : std::as_const(m_originalItems)) {
         const QString &text = item->filterText();
 
         // Direct match?