Support Postgres array size specification

[judahrand]

Is your feature request related to a problem? Please describe.

We have some SQL which defines array lengths in the schema for the purposes of documentation (since Postgres currently ignores the length in the implementation). sqlglot is unable to parse this SQL.

sqlglot.parse_one('CREATE TABLE t (col int[3])', dialect='postgres')

Describe the solution you'd like

Support the array length syntax.