Fix the public schema's permissions in a separate test script.

Fix the public schema's permissions in a separate test script.

In the wake of commit b073c3ccd, it's necessary to grant create
permissions on the public schema to PUBLIC to get many of the
core regression test scripts to pass.  That commit did so via the
quick-n-dirty expedient of adding the GRANT to the tablespace test,
which runs first.  This is problematic for single-machine
replication testing, though.  The least painful way to run the
regression tests on such a setup is to skip the tablespace test,
and that no longer works.

To fix, let's invent a separate "test_setup" script to run first,
and put the GRANT there.  Revert b073c3ccd's changes to
the tablespace.source files.

In the future it might be good to try to reduce coupling between
the various test scripts by having test_setup create widely-used
objects, with the goal that most of the scripts could run after
having run only test_setup.  That's going to take some effort,
so this commit just addresses my immediate pain point.

Discussion: https://postgr.es/m/1363170.1639763559@sss.pgh.pa.us