doc: Update SQL features/conformance information to SQL:2023
Optional subfeatures have been changed to top-level features, so there
is a bit of a churn in the list for that.
Some existing functions have been added to the standard, so they are
moved from the "other" to the "standard" lists in their sections.
Discussion: https://www.postgresql.org/message-id/flat/
63f285d9-4ec8-0c9e-4bf5-
e76334ddc0af@enterprisedb.com