pgsql: Refactor parsing rules for option lists of EXPLAIN, VACUUM and A

Refactor parsing rules for option lists of EXPLAIN, VACUUM and ANALYZE

Those three commands have been using the same grammar rules to handle a
a list of parenthesized options.  This refactors the code so as they use
the same parsing rules, shaving some code.  A future commit will make
use of those option parsing rules for more utility commands, like
REINDEX and CLUSTER.

Author: Alexey Kondratov, Justin Pryzby
Discussion: https://postgr.es/m/8a8f5f73-00d3-55f8-7583-1375ca8f6a91@postgrespro.ru

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/873ea9ee692e7829614f913685db540b17998ba6

Modified Files
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src/backend/parser/gram.y | 61 +++++++++++------------------------------------
1 file changed, 14 insertions(+), 47 deletions(-)