pgsql: Stabilize recently-added information_schema test queries.

Stabilize recently-added information_schema test queries.

These queries could show unexpected entries if the core system,
or concurrently-running test scripts, created any functions that
would appear in the information_schema views. Restrict them
to showing functions belonging to this test's schema, as the
far-older nearby test case does.

Per experimentation with conversion of some built-in functions
to SQL-function-body style.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/3157cbe974846729d49a1ee081944eee1839bdd8

Modified Files
--------------
src/test/regress/expected/create_function_3.out | 14 +++++++++++---
src/test/regress/sql/create_function_3.sql | 14 +++++++++++---
2 files changed, 22 insertions(+), 6 deletions(-)