pgsql: Doc: fix missing/bogus documentation of range_intersect_agg().

Doc: fix missing/bogus documentation of range_intersect_agg().

The form taking anymultirange had not been documented.  This was
fixed in HEAD in b21c4cf95, but that should have been back-patched
to v14 since the function was added there.  Do so now.

Also, the form taking anyrange was incorrectly documented as
returning anymultirange, when it returns anyrange.

Remove b21c4cf95 from the v15 release notes, since it no longer
qualifies as new-in-v15.

Noted by Shay Rojansky.

Discussion: https://postgr.es/m/CADT4RqAktzP7t6SFf0Xqm9YhahzvsmxFbzXe-gFOd=+_CHm0JA@mail.gmail.com

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/9f2d1946d4b41a27cb5b62da7a5f070acc62cd4e

Modified Files
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doc/src/sgml/func.sgml | 5 +++++
1 file changed, 5 insertions(+)