Issue #21715: Extracted shared complicated code in the _io module to new

_PyErr_ChainExceptions() function.

diff --cc Include/pyerrors.h
Simple merge

diff --cc Modules/_io/_iomodule.c
Simple merge

diff --cc Modules/_io/bufferedio.c
Simple merge

diff --cc Modules/_io/textio.c
Simple merge

diff --cc Python/errors.c
Simple merge