Redshift dialect: regtype 'int4' parses as a column with an alias, not a typed literal #2962

Redshift, like Postgres, accepts the generic typed-literal form type 'string' for any type name. sqlparser parses it as a typed string only for types it knows, such as regclass. For other type names it reads the type as a column and the string as an alias.

select regtype 'int4'

• sqlparser 0.64.0: ExprWithAlias { expr: Identifier("regtype"), alias: Ident { value: "int4", quote_style: Some('\'') } }, i.e. the column regtype aliased as 'int4'.
• Redshift: one row, integer, i.e. the literal 'int4' cast to regtype.

Other forms behave the same way: select "regtype" 'int4' returns integer and select regproc 'version' returns version on Redshift, while sqlparser parses both as aliased columns. select regclass 'pg_user' already parses as a typed string because sqlparser has a Regclass data type.

Postgres documents the syntax under "Constants of Other Types" (https://www.postgresql.org/docs/8.0/sql-syntax.html#SQL-SYNTAX-CONSTANTS-GENERIC), and Redshift is based on PostgreSQL 8.0.2 (https://docs.aws.amazon.com/redshift/latest/dg/c_redshift-and-postgres-sql.html).