Fix performance issue in deadlock-parallel isolation test.

Fix performance issue in deadlock-parallel isolation test.

With debug_discard_caches = 1, the runtime of this test script
increased by about a factor of 10 after commit 0dca5d68d.  That's
causing some of our buildfarm animals to fail with a timeout.

The reason for the increased time is that now we are re-planning
some intentionally-non-inlineable SQL functions on every execution,
where the previous coding held onto the original plans throughout
the outer query.  The previous behavior was arguably quite buggy,
so I don't think 0dca5d68d deserves blame here.  But we would
like this test script to not take so long.

To fix, instead of forcing a "parallel safe" label via a
non-inlineable SQL function, apply it directly to the advisory-lock
functions by making internal-language aliases for them.  A small
problem is that the advisory-lock functions return void but this
test would really like them to return integer 1.  I cheated here by
declaring the aliases as returning "int".  That's perhaps undue
familiarity with the implementation of PG_RETURN_VOID(), but that
hasn't changed in twenty years and is unlikely to do so in the next
twenty.  That gets us an integer 0 result, and then an inline-able
wrapper to convert that to an integer 1 allows the rest of the script
to remain unchanged.

For me, this reduces the runtime with debug_discard_caches = 1
by about 100x, making the test comfortably faster than before
instead of slower.

Discussion: https://postgr.es/m/136163.1744179562@sss.pgh.pa.us