Add PostgreSQL specfic "CREATE TYPE t AS ENUM (...)" support.

[caldwell]

See: https://www.postgresql.org/docs/current/sql-createtype.html

I implemented this as a separate Statement::CreateTypeAsEnum { name, labels } so it wouldn't be as invasive to the existing Statement::CreateType (which I would imagine helps forwards/backwards compatibility for the crate's users).

I used the PostgreSqlDialect's comment as a blueprint but that means that the generic dialect doesn't get this feature (unless I'm missing something). I didn't see parse_statement() implemented in GenericDialect though I suppose it could be (and call out to other dialects' parse_statement()s). I didn't want to set that precedent without asking.

[coveralls]

Pull Request Test Coverage Report for Build 11432831633

Details

• 34 of 36 (94.44%) changed or added relevant lines in 3 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.005%) to 89.392%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/dialect/postgresql.rs	18	19	94.74%
tests/sqlparser_postgres.rs	15	16	93.75%
<!--	Total:	34	36	94.44%	-->

Files with Coverage Reduction	New Missed Lines	%
src/ast/ddl.rs	1	87.46%
tests/sqlparser_postgres.rs	1	88.57%
<!--	Total:	2		-->

Totals
Change from base Build 11429400839:	0.005%
Covered Lines:	30497
Relevant Lines:	34116

---

💛 - Coveralls

[alamb]

@caldwell have you had a chance to consider @iffyio 's suggestions above?

[caldwell]

Apologies, not yet. I'll try to look at it today.

[caldwell]

I amended my commit per @iffyio's suggestions. Thanks for taking the time to look at it and apologies again for taking too long to respond.

[alamb]

I amended my commit per @iffyio's suggestions. Thanks for taking the time to look at it and apologies again for taking too long to respond.

no worries -- thank you!

[caldwell]

I pushed a fix for the formatting test failure.

[alamb]

🚀