pgsql: Handle sequences in preprocess_pubobj_list

Handle sequences in preprocess_pubobj_list

Commit 75b1521dae added support for logical replication of sequences,
including grammar changes, but it did not update preprocess_pubobj_list
accordingly. This can cause segfaults with "continuations", i.e. when
command specifies a list of objects:

CREATE PUBLICATION p FOR SEQUENCE s1, s2;

Reported by Amit Kapila, patch by me.

Reported-by: Amit Kapila
Discussion: https://postgr.es/m/CAA4eK1JxDNKGBSNTyN-Xj2JRjzFo+ziSqJbjH==vuO0YF_CQrg@mail.gmail.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/002c9dd97a0c874fd1693a570383e2dd38cd40d5

Modified Files
--------------
src/backend/parser/gram.y | 27 ++++++++++++++++++++++++++-
src/test/regress/expected/publication.out | 18 ++++++++++++++++++
src/test/regress/sql/publication.sql | 16 ++++++++++++++++
3 files changed, 60 insertions(+), 1 deletion(-)