[3.12] gh-107298: Docs: add targets for some :c:member: and :c:macro: references (GH-107316) (GH-107332)

Add targets for PyStructSequence_Desc and PyStructSequence_Field members
and macros like Py_EQ.
Fix target for Py_RETURN_RICHCOMPARE.
(cherry picked from commit abec9a1b20b70d8ced401d59fc4f02b331c6568b)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>