libstdc++: [_Hashtable] Insert range of types convertible to value_type PR 105717

libstdc++: [_Hashtable] Insert range of types convertible to value_type PR 105717

Fix insertion of range of instances convertible to value_type.

libstdc++-v3/ChangeLog:

	PR libstdc++/105717
	* include/bits/hashtable_policy.h (_ConvertToValueType): New.
	* include/bits/hashtable.h (_Hashtable<>::_M_insert_unique_aux): New.
	(_Hashtable<>::_M_insert(_Arg&&, const _NodeGenerator&, true_type)): Use latters.
	(_Hashtable<>::_M_insert(_Arg&&, const _NodeGenerator&, false_type)): Likewise.
	(_Hashtable(_InputIterator, _InputIterator, size_type, const _Hash&, const _Equal&,
	const allocator_type&, true_type)): Use this.insert range.
	(_Hashtable(_InputIterator, _InputIterator, size_type, const _Hash&, const _Equal&,
	const allocator_type&, false_type)): Use _M_insert.
	* testsuite/23_containers/unordered_map/cons/56112.cc: Check how many times conversion
	is done.
	* testsuite/23_containers/unordered_map/insert/105717.cc: New test.
	* testsuite/23_containers/unordered_set/insert/105717.cc: New test.