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: I601bf70f020f511019ed28731ba53b14b765dbf0
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>