This is needed so that renumber_oids.pl can handle renumbering
shared catalog declarations, which need to provide C macros for
the OIDs of the shared toast table and index. The previous
method of writing a C macro separately was error-prone anyway.
Also teach renumber_oids.pl about DECLARE_UNIQUE_INDEX_PKEY,
as we missed doing when inventing that macro.
There are no changes to postgres.bki here, so no need for a
catversion bump.
Discussion: https://postgr.es/m/2995325.1650487527@sss.pgh.pa.us
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