pgsql: test_aio: Add basic tests for StartReadBuffers()

test_aio: Add basic tests for StartReadBuffers()

Upcoming commits will change StartReadBuffers() and its building blocks,
making it worthwhile to directly test StartReadBuffers().

Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Discussion: /messages/by-id/zljergweqti7x67lg5ije2rzjusie37nslsnkjkkby4laqqbfw@3p3zu522yykv

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/020c02bd90896066964d173139b3adb154ec7426

Modified Files
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src/test/modules/test_aio/t/001_aio.pl | 243 ++++++++++++++++++++++++++++
src/test/modules/test_aio/test_aio--1.0.sql | 7 +
src/test/modules/test_aio/test_aio.c | 229 ++++++++++++++++++++++++--
3 files changed, 469 insertions(+), 10 deletions(-)