Add helper that allows us to determine the argument list and return type
of a functor. This triggers a compile time error if the functor has
operator()() overloads (we only support zero-argument call operators, but
there might be const/noexcept variations). Use that helper to declare a
ZeroArgFunctor type which also declares a ReturnType and Arguments alias.
Add a Callable alias that now combines FunctionPointer and ZeroArgFunctor
into a single type that we can then use to merge the specializations of
QMetaObject::invokeMethod.
[ChangeLog][Potentially source-incompatible changes] Using a functor
with several operator() overloads in QMetaObject::invokeMethod now causes
a compile time error. Qt would previously ignore const and noexcept
overloads and always call the mutable version on a copy of the functor.
Change-Id: I3eb62c1128014b729575540deab615469290daeb
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
3bf5b5f894