Add "DROP TYPE" support.

[caldwell]

See: https://www.postgresql.org/docs/current/sql-droptype.html
https://learn.microsoft.com/en-us/sql/t-sql/statements/drop-type-transact-sql?view=sql-server-ver16
https://docs.oracle.com/en/database/oracle/oracle-database/19/sqlrf/DROP-TYPE.html

According to the postgresql docs (above), their implementation is from ansi with only the IF EXISTS being an extension. mssql supports the IF EXISTS extension as well though it looks like Oracle doesn't.

I implemented this as a new ObjectType::Type which lets the existing Statement::Drop handle it generically.

[alamb]

Makes sense to me . Thank you @caldwell

cc @iffyio

[coveralls]

Pull Request Test Coverage Report for Build 11221669025

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 34 of 40 (85.0%) changed or added relevant lines in 2 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.001%) to 89.307%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tests/sqlparser_common.rs	32	38	84.21%

Files with Coverage Reduction	New Missed Lines	%
tests/sqlparser_common.rs	1	89.56%

Totals
Change from base Build 11186281805:	-0.001%
Covered Lines:	30026
Relevant Lines:	33621

---

💛 - Coveralls

[iffyio]

LGTM!

[alamb]

🚀