pgsql: Rework grammar for REINDEX

Rework grammar for REINDEX

The part of grammar have grown needlessly duplicative and more complex
that necessary.  Rewrite.

Reviewed-by: Michaël Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/20220721174212.cmitjpuimx6ssyyj@alvherre.pgsql

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/83011ce7d7f42b744a93d2b0819597d0aa94e9cc

Modified Files
--------------
doc/src/sgml/ref/reindex.sgml              |  3 +-
src/backend/parser/gram.y                  | 85 ++++++++++--------------------
src/test/regress/expected/create_index.out |  6 +++
src/test/regress/sql/create_index.sql      |  2 +
4 files changed, 38 insertions(+), 58 deletions(-)