libstdc++: Use std::move for iterator in ranges::fill [PR117094]

Input iterators aren't required to be copyable.

libstdc++-v3/ChangeLog:

	PR libstdc++/117094
	* include/bits/ranges_algobase.h (__fill_fn): Use std::move for
	iterator that might not be copyable.
	* testsuite/25_algorithms/fill/constrained.cc: Check
	non-copyable iterator with sized sentinel.