`includes` uses SQL parsing when String joins are involved.

This is a partial revert of 22b3481ba2aa55fad1f9a5db94072312b345fb55.
The current implementation of `references_eager_loaded_tables?` needs to know
every table involved in the query. With the current API this is not possible
without SQL parsing.

While a2dab46cae35a06fd5c5500037177492a047c252 deprecated SQL parsing for `includes`.
It did not issue deprecation warnings when String joins are involved. This resulted
in a breaking change after the deprecated behavior was removed (22b3481ba2aa55fad1f9a5db94072312b345fb55).

We will need to rethink the usage of `includes`, `preload` and `eager_load` but for now,
this brings back the old *working* behavior.
Merge pull request #14226 from senny/14109_partial_revert

`includes` uses SQL parsing when String joins are involved.