This change was breaking the Railties tests. See
https://travis-ci.org/rails/rails/jobs/9865969

The deprecation message was removed on 50cbc03d but the code was not.

If the `db/` directory is not present on a remote machine it will blow up in unexpected ways with error messages that do not indicate there is a missing directory:

```
SQLite3::CantOpenException: unable to open database file
```

This PR checks to see if a directory exists for the sqlite3 file and if not creates it for you.

This PR is an alternative to #11692 as suggested by @josevalim

`result_metadata` returns a new object each time it is called, so calling `result_metadata.free` is essentially a noop.  Instead call `free` directly on the metadata when we're done with it.

When mixing postgresql and another adapter like sqlite3 (for dev and test
respectively), the task `db:test:prepare` will fail due to the `enable_extension`
method not being defined in the abstract adapter. This patch simply adds an
empty definition to prevent it.

Closes: #11706

decouple the builder classes from the model.  Builder objects should be
easier to reuse now.

`configure_dependency` actually defined callbacks, so rename the method
and move it to the appropriate method.

- Use symbols rather than strings where possible to avoid extra object construction
- Use destructive methods where possible to avoid extra object construction
- Use array union rather than concat followed by uniq
- Use shorthand block syntax where possible
- Use consistent multiline block styles, method names, method parenteses style, and spacing

This reverts commit 1468a4b8.