database-specific DDL for schema export

It would be useful to be able to register platform-specific DDL for execution by the schema management tooling. The most logical place for this is XML. Something like:

```xml

major-version
12
CREATE OR REPLACE FUNCTION ...
DROP FUNCTION ...

```

This came up as being potentially useful for the TCK.

Hibernate already has something quite similar to this.

Start by reviewing the schema management tooling and the TCK use case described in the issue, then compare Hibernate's similar capability. The issue is complete when the project has agreed how XML registers database-specific create and drop DDL, including product and major-version matching, and how the tooling executes it.

Written by the indexing model from the issue text.