pgsql: Add test_dsa module.

Add test_dsa module.

This covers basic calls within a single backend process, and also
calling dsa_allocate() or dsa_get_address() while in a different
resource owners. The latter case was fixed by the previous commit.

Discussion: https://www.postgresql.org/message-id/11b70743-c5f3-3910-8e5b-dd6c115ff829%40gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/325f54033e59499cfc087932f68eec5356061640

Modified Files
--------------
src/test/modules/Makefile                       |   1 +
src/test/modules/meson.build                    |   1 +
src/test/modules/test_dsa/Makefile              |  23 +++++
src/test/modules/test_dsa/expected/test_dsa.out |  13 +++
src/test/modules/test_dsa/meson.build           |  33 +++++++
src/test/modules/test_dsa/sql/test_dsa.sql      |   4 +
src/test/modules/test_dsa/test_dsa--1.0.sql     |  12 +++
src/test/modules/test_dsa/test_dsa.c            | 113 ++++++++++++++++++++++++
src/test/modules/test_dsa/test_dsa.control      |   4 +
9 files changed, 204 insertions(+)