Previously, the DatabaseDriver enumeration contained entries for
some databases without having dependency management for the database
driver dependency. This leads to the possibility of a user inadvertently
using the wrong version of a driver where the class names do not match
those listed in the enumeration. A further problem is that we do not
test that the class names listed in the enumeration match the
names of Driver and XADataSource implementations in the database driver.

This commit completes the database driver dependency management so that
dependency management is provided for every driver that is both listed
in DatabaseDriver and available in Maven Central. It also adds tests
for DatabaseDriver that ensures that each class that is listed exists
and implements the required interface (java.sql.Driver or
javax.sql.XADataSource).

Closes gh-4946