Add tab completion for CREATE SCHEMA in psql

Add tab completion for CREATE SCHEMA in psql

The following patterns are added for CREATE SCHEMA:
- AUTHORIZATION, without a schema name or after a schema name.
- Possible list of owner roles after AUTHORIZATION.
- CREATE and GRANT within the supported set of commands.
- Correct object types supported in an embedded CREATE SCHEMA command.

While on it, this commit adjusts the completion done after CREATE
UNLOGGED:
- Addition of SEQUENCE.
- Avoid suggesting MATERIALIZED VIEW in CREATE TABLE.

Author: Dagfinn Ilmari Mannsåker
Reviewed-by: Suraj Khamkar, Michael Paquier
Discussion: https://postgr.es/m/8735snihmz.fsf@wibble.ilmari.org