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/libs/utils/fancylineedit.cpp

@@ -509,7 +509,7 @@ void FancyLineEdit::validate()
 
     // Check buttons.
     if (d->m_oldText.isEmpty() || t.isEmpty()) {
-        for (auto &button : qAsConst(d->m_iconbutton)) {
+        for (auto &button : std::as_const(d->m_iconbutton)) {
             if (button->hasAutoHide())
                 button->animateShow(!t.isEmpty());
         }