libstdc++: Implement LWG 3564 for ranges::transform_view
The _Iterator<true> type returned by begin() const uses const F& to
transform the elements, so it should use const F& to determine the
iterator's value_type and iterator_category as well.
This was accepted into the WP in July 2022.
libstdc++-v3/ChangeLog:
* include/std/ranges (transform_view:_Iterator): Use const F&
to determine value_type and iterator_category of
_Iterator<true>, as per LWG 3564.
* testsuite/std/ranges/adaptors/transform.cc: Check value_type
and iterator_category.
Reviewed-by: Patrick Palka <ppalka@redhat.com>