pgsql: Fix CREATE DATABASE so we can pg_upgrade DBs with OIDs above 2^3

Fix CREATE DATABASE so we can pg_upgrade DBs with OIDs above 2^31.

Commit aa0105141 repeated one of the oldest mistakes in our book:
thinking that OID is the same as int32. It isn't of course, and
unsurprisingly the first person who came along with a database
OID above 2 billion broke it. Repair.

Per bug #17677 from Sergey Pankov. Back-patch to v15.

Discussion: https://postgr.es/m/17677-a99fa067d7ed71c9@postgresql.org

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/2c6d43650d16d91a3e731d236315beffd98db729

Modified Files
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src/backend/commands/dbcommands.c | 2 +-
src/backend/commands/define.c | 33 +++++++++++++++++++++++++++++++++
src/backend/parser/gram.y | 4 ++--
src/include/commands/defrem.h | 1 +
4 files changed, 37 insertions(+), 3 deletions(-)