Back-patch "Refactor code in tablecmds.c to check and process tablespace moves"

Back-patch "Refactor code in tablecmds.c to check and process tablespace moves"

Back-patch commits 4c9c359d38ff1e2de388eedd860785be6a49201c and
24843297a96d7be16cc3f4b090aacfc6e5e6839e to v13 and v12.  Before those
commits, we held the modifiable copy of the relation's pg_class row
throughout a table_relation_copy_data().  That can last long enough to
copy MaxBlockNumber of data.  A subsequent fix will hold LockTuple() for
the lifespan of that modifiable copy.  By back-patching this first, we
avoid a needless long-duration LOCKTAG_TUPLE.

Discussion: https://postgr.es/m/20231027214946.79.nmisch@google.com