pg_upgrade: Parallelize data type checks.

pg_upgrade: Parallelize data type checks.

This commit makes use of the new task framework in pg_upgrade to
parallelize the checks for incompatible data types, i.e., data
types whose on-disk format has changed, data types that have been
removed, etc.  This step will now process multiple databases
concurrently when pg_upgrade's --jobs option is provided a value
greater than 1.

Reviewed-by: Daniel Gustafsson, Ilya Gladyshev
Discussion: https://postgr.es/m/20240516211638.GA1688936%40nathanxps13