This changes CLUSTER and REINDEX so as a parenthesized grammar becomes
possible for options, while unifying the grammar parsing rules for
option lists with the existing ones.

This is a follow-up of the work done in 873ea9ee for VACUUM, ANALYZE and
EXPLAIN.  This benefits REINDEX for a potential backend-side filtering
for collatable-sensitive indexes and TABLESPACE, while CLUSTER would
benefit from the latter.

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