catalog: Populate PostgreSQL type lengths

[sjwiesman]

Motivation

pg_type.typlen and pg_attribute.attlen are always NULL in Materialize. pgjdbc derives DatabaseMetaData.getMaxColumnNameLength() and getMaxTableNameLength() from the typlen of name, so it reports -1 instead of 63. Trino's PostgreSQL connector treats a non-positive identifier limit as an error, which breaks join pushdown (and table creation) against Materialize.

Description

mz_internal.mz_type_pg_metadata gains a nullable typlen column, and pg_type reads typlen from it instead of NULL::int2. pg_attribute.attlen is derived from pg_type.typlen, so it is populated too.

The value comes from resolving the catalog type to its SqlScalarType and asking mz_pgrepr::Type for its length. That is the same value pgwire already sends as type_len in RowDescription, so the catalog and the wire protocol agree. Type::from_oid was not used because it does not know name, aclitem, _record, and a few other built-ins.

Types with no PostgreSQL counterpart keep a NULL typlen: pseudo-types (anyelement, ...), _record, and Materialize-only types such as uint2 and list. mz_type_pg_metadata describes the PostgreSQL view of a type, so inventing lengths for types PostgreSQL does not have would misreport.

Because mz_type_pg_metadata is a builtin table with a new column, it gets a replacement builtin schema migration.

Verification

• test_compare_builtins_postgres now also asserts that every built-in type with a PostgreSQL counterpart reports the same typlen as PostgreSQL.
• pg_catalog_attribute.slt checks typlen for a spread of fixed-length, variable-length, pseudo, and Materialize-only types, and attlen for table columns.
• The Java smoketest asserts that pgjdbc reports 63 for the maximum column and table name lengths.
• cockroach/orms.slt, catalog_server_explain.slt and mz_catalog_server_index_accounting.slt are updated for the populated attlen and the changed view definition.
• Manually, Trino's PostgreSQL connector pushes joins down to Materialize with this change, and fails to do so without it.

Release notes

This release will report PostgreSQL type lengths in pg_type.typlen and pg_attribute.attlen, which lets JDBC-based tools such as Trino read identifier length limits correctly.

[antiguru]

Looks good, please update the PR body before merging.

[ggevay]

LGTM