libstdc++: Reduce ranges::minmax/minmax_element comparison complexity

libstdc++: Reduce ranges::minmax/minmax_element comparison complexity

This rewrites ranges::minmax and ranges::minmax_element so that it
performs at most 3*N/2 many comparisons, as required by the standard.
In passing, this also fixes PR100387 by avoiding a premature std::move
in ranges::minmax and in std::shift_right.

	PR libstdc++/100387

libstdc++-v3/ChangeLog:

	* include/bits/ranges_algo.h (__minmax_fn::operator()): Rewrite
	to limit comparison complexity to 3*N/2.
	(__minmax_element_fn::operator()): Likewise.
	(shift_right): Avoid premature std::move of __result.
	* testsuite/25_algorithms/minmax/constrained.cc (test04, test05):
	New tests.
	* testsuite/25_algorithms/minmax_element/constrained.cc (test02):
	Likewise.