pgsql: parser: centralize common auxiliary productions

parser: centralize common auxiliary productions

Things like "opt_name" can well be shared by various commands rather
than there being multiple definitions of the same thing. Rename these
productions and move them to appear together in gram.y, which may
improve chances of reuse in the future.

Discussion: https://postgr.es/m/20220721174212.cmitjpuimx6ssyyj@alvherre.pgsql

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/7d158e8cb44b602ab76a3660b9f5f5c5c5992a1f

Modified Files
--------------
src/backend/parser/gram.y | 89 +++++++++++++++++++++++------------------------
1 file changed, 44 insertions(+), 45 deletions(-)