pgsql: Improve coverage of ruleutils.c for SQLValueFunctions

Improve coverage of ruleutils.c for SQLValueFunctions

While looking at how these are handled in the parser and the executor, I
have noticed that there is no test coverage for most of these when
reverse-engineering an expression for a SQLValueFunction node in
ruleutils.c, including how these are reparsed when included in a FROM
clause. Some hacking in this area has showed me that these could break
easily, so add some coverage to track the existing compatibility.

Extracted from a much larger patch by me.

Discussion: https://postgr.es/m/YzaG3MoryCguUOym@paquier.xyz

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2e0d80c5bb722fb49a4cdc44b0c715ec77c83f79

Modified Files
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src/test/regress/expected/create_view.out | 82 ++++++++++++++++++++++++++++++-
src/test/regress/sql/create_view.sql | 33 ++++++++++++-
2 files changed, 112 insertions(+), 3 deletions(-)