sql: add the ability to access a column from the results of an SRF

[jseldess]

PR: cockroachdb/cockroach#24832

From release notes:

Set Returning Functions (SRF) can now be accessed using (SRF).x, where x is the name of a column returned from the SRF or a *. For example, SELECT (information_schema._pg_expandarray(ARRAY['c', 'b', 'a'])).x and SELECT (information_schema._pg_expandarray(ARRAY['c', 'b', 'a'])).* are now both valid. Also, the naming of the resulting columns from SRFs now provide more information about the resulting tuple. [#24832][#24832] {% comment %}doc{% endcomment %}

[rmloveland]

Relates to:

• Document SQL updates in support of Hibernate's use of _pg_expandarray #3142
• Support _pg_expandarray #2980