#2821 replacing `@group` annotations with proper references, since DBAL-* issues are from JIRA, not Github

Added upgrade notice about BC break.
Cleanups

Changed DBALException::invalidPlatformSpecified() exception to be more detailed about what was given.

Fixed cs issues

If you pass a null to the where array of update or delete it's
pretty obvious what you want.

Most (all?) databases won't match anything if you actually try
to compare with NULL making this a silent failure without it.

This mocks connect(), sets the internal _conn to an object, then calls close, which
should re-set _conn back to null. The getWrappedConnection() call gives us access
to _conn, but does NOT trigger a re-connect, since we mocked connect() to do nothing.
Ultimately, if _conn is unset, calling getWrappedConnection() will error. If _conn
is not set to null, the test will fail. This tests all the cases.