Parsing "CREATE MATERIALIZED VIEW IF NOT EXISTS ..." is not supported

[zaza]

Parsing a string creating materialized view with "IF NOT EXISTS" clause fails with an error. It appears that Feature.createViewMaterializedIfNotExists is missing, which would be similar to createViewMaterialized and createTableIfNotExists.

[wumpz]

This one should be done after the materialized fine-tuning you proposed, right? However, this validation framework is somehow behind the normal JSqlParser development. So there are more missing pieces for sure.

[zaza]

I created #1690 but please let me know if I missed anything. This is my first contribution to this project. I do plan to tackle the other issues I recently reported, but wanted to do it one by one.