[PATCH] use separate PartitionedRelOptions structure to store partitioned table options

Hi!

This message is follow up to the "Get rid of the StdRdOptions" patch thread:
https://www.postgresql.org/message-id/2620882.s52SJui4ql@x200m

I've split patch into even smaller parts and commitfest want each patch in
separate thread. So it is new thread.

The idea of this patch is following: If you read the code, partitioned tables
do not have any options (you will not find RELOPT_KIND_PARTITIONED in
boolRelOpts, intRelOpts, realRelOpts, stringRelOpts and enumRelOpts in
reloption.c), but it uses StdRdOptions to store them (these no options).

If partitioned table is to have it's own option set (even if it is empty now)
it would be better to save it into separate structure, like it is done for
Views, not adding them to StdRdOptions, like current code hints to do.

So in this patch I am creating a structure that would store partitioned table
options (it is empty for now as there are no options for this relation kind),
and all other code that would use this structure as soon as the first option
comes.

I think it is bad idea to suggest option adder to ad it to StdRdOption, we
already have a big mess there. Better if he add it to an new empty structure.

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