Enable listing SQL function with session property

[caithagoras]

Resolves #13864

== RELEASE NOTES ==
General Changes
* Support hiding user-defined SQL functions in ``SHOW FUNCTIONS`` with session property ``list_built_in_functions_only``.
  This can also be achieved by configuration property ``list-built-in-functions-only``, which is repurposed from ``list-non-built-in-functions``.

[rongrong]

Let's call it list_all_functions?

[caithagoras]

What about list_sql_functions, list_user_defined_functions, or list_udfs if you think the current name is cumbersome.

For people who don't have context, it's not clear from reading the name what the difference is between "all functions" and "not all functions", and any of those 3 names at least gives some hint.

[rongrong]

But is this only going to list sql functions? it will list all functions right? Unless you are planning to make it an enum and allow only listing certain functions. Another way to configure this is to have it as list_static_functions_only.

[caithagoras]

Since we're using "built in function" as the language in our code, I'm updating the PR to use list_built_in_functions_only.

[caithagoras]

@rongrong Comments addressed.

[ajaygeorge]

LGTM.
Try squashing the commits before final merge.

[caithagoras]

Commit squashed. Release notes updated.

[caithagoras]

@rongrong comments addressed