pgsql: Minor fixes for test_bitmapset.c

Minor fixes for test_bitmapset.c

1. Make it so test_random_operations() can accept a NULL to have the
function select a random seed.
2. Widen the seed parameter of test_random_operations() to bigint.
Without that, it'll be impossible to run the function with a seed
which was selected by GetCurrentTimestamp(), and if a randomly
selected seed ever results in a failure, we'll likely want to run
with the same seed to debug the issue.
3. Report the seed in the error messages in test_random_operations().
If the buildfarm were ever to fail there, we'd certainly want to know
what this was.
4. Add CHECK_FOR_INTERRUPTS() to test_random_operations(). Someone might
run with a large num_ops and they'd have no way to cancel the query.
5. Minor cosmetic fixes; header order and whitespace issue.

To allow #1, the STRICT modifier had to be removed. The additional
prechecks were added as I didn't see how else to handle someone passing
those parameters as NULL.

Author: David Rowley <dgrowleyml(at)gmail(dot)com>
Reviewed-by: Greg Burd <greg(at)burd(dot)me>
Discussion: https://postgr.es/m/CAApHDvrDW9W72vAr7h7XeCu7+Qz-_Vff02Q+RPPuVeM0Qf0MCw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5142f0093e648d1a32fdcc7c835d17fa103e1239

Modified Files
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.../test_bitmapset/expected/test_bitmapset.out | 2 +-
.../modules/test_bitmapset/sql/test_bitmapset.sql | 2 +-
.../modules/test_bitmapset/test_bitmapset--1.0.sql | 4 +--
src/test/modules/test_bitmapset/test_bitmapset.c | 42 +++++++++++++++++-----
4 files changed, 37 insertions(+), 13 deletions(-)