libstdc++: Fix forwarding in __take/drop_of_repeat_view [PR112453]

libstdc++: Fix forwarding in __take/drop_of_repeat_view [PR112453]

We need to respect the value category of the repeat_view passed to these
two functions when accessing the view's _M_value member.  This revealed
that the space-efficient partial specialization of __box lacks && overloads
of operator* to match those of the primary template (inherited from
std::optional).

	PR libstdc++/112453

libstdc++-v3/ChangeLog:

	* include/std/ranges (__detail::__box<_Tp>::operator*): Define
	&& overloads as well.
	(__detail::__take_of_repeat_view): Forward __r when accessing
	its _M_value member.
	(__detail::__drop_of_repeat_view): Likewise.
	* testsuite/std/ranges/repeat/1.cc (test07): New test.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>