This commit deprecates several undocumented top-level FactoryBot
methods:
* callbacks
* configuration
* constructor
* initialize_with
* register_sequence
* resent_configuration
* skip_create
* to_create
factory_bot users are not meant to access these methods directly.
Instead they are available for internal use through the new Internal
module introduced in #1262.
---
While addressing the new deprecation warnings, I tried to make the
delegation a bit more consistent, always delegating to
`FactoryBot::Internal`.
This involved requiring "factory_bot/internal" sooner. To avoid having
to fight with the order of requires and potential circular dependencies,
I moved the default strategy and callback registration out of constants
(this is how they used to be before #1297), so it doesn't matter if
those strategies are loaded before the `Internal` module. I also deleted
a pair of tests that were using these constants - these strategies and
callbacks are covered elsewhere in our test suite, and I don't think
these tests were adding much value (they missed #1379, for example).
