libstdc++: Limit memory allocation in stable_sort/inplace_merge (PR 83938)

libstdc++: Limit memory allocation in stable_sort/inplace_merge (PR 83938)

Reduce memory allocation in stable_sort/inplace_merge algorithms to what is needed
by the implementation.

Co-authored-by: John Chang  <john.chang@samba.tv>
libstdc++-v3/ChangeLog:

	PR libstdc++/83938
	* include/bits/stl_tempbuf.h (get_temporary_buffer): Change __len
	computation in the loop to avoid truncation.
	* include/bits/stl_algo.h:
	(__inplace_merge): Take temporary buffer length from smallest range.
	(__stable_sort): Limit temporary buffer length.
	* testsuite/25_algorithms/inplace_merge/1.cc (test4): New.
	* testsuite/performance/25_algorithms/stable_sort.cc: Test stable_sort
	under different heap memory conditions.
	* testsuite/performance/25_algorithms/inplace_merge.cc: New test.