libstdc++: Handle extended alignment in std::get_temporary_buffer [PR105258]

This adds extended alignment support to std::get_temporary_buffer etc.
so that when std::stable_sort uses a temporary buffer it works for
overaligned types.

Also simplify the _Temporary_buffer type by using RAII for the
allocation, via a new data member. This simplifies the _Temporary_buffer
constructor and destructor by makingthem only responsible for
constructing and destroying the elements, not managing the memory.

libstdc++-v3/ChangeLog:

	PR libstdc++/105258
	* include/bits/stl_tempbuf.h (__detail::__get_temporary_buffer):
	New function to do allocation for get_temporary_buffer, with
	extended alignment support.
	(__detail::__return_temporary_buffer): Support extended
	alignment.
	(get_temporary_buffer): Use __get_temporary_buffer.
	(return_temporary_buffer): Support extended alignment. Add
	deprecated attribute.
	(_Temporary_buffer): Move allocation and deallocation into a
	subobject and remove try-catch block in constructor.
	(__uninitialized_construct_buf): Use argument deduction for
	value type.
	* testsuite/20_util/temporary_buffer.cc: Add dg-warning for new
	deprecated warning.
	* testsuite/25_algorithms/stable_sort/overaligned.cc: New test.

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