These are all available in Trainer.

Remove duplicate/unused code

…tic class variable (#3297)

…ment (#3294)

In multilingual models, the target language is specified via the
`--language_idx` argument. However, the `tts` CLI also accepts a `--language`
argument for use with Coqui Studio, so it is easy to choose the wrong one,
resulting in the following confusing error at synthesis time:

```
AssertionError:  ❗ Language None is not supported. Supported languages are
['en', 'es', 'fr', 'de', 'it', 'pt', 'pl', 'tr', 'ru', 'nl', 'cs', 'ar',
'zh-cn', 'hu', 'ko', 'ja']
```

This commit adds a better error message when `--language` is passed for a
non-studio model.

Fixes #3270, fixes #3291

Previously, the text was wrapped in an additional set of quotes that was passed
to Espeak. This could result in different phonemization in certain edges and
caused the insertion of an initial separator "_" that had to be removed.
Compare:
$ espeak-ng -q -b 1 -v en-us --ipa=1 '"A"'
_ˈɐ
$ espeak-ng -q -b 1 -v en-us --ipa=1 'A'
ˈeɪ

Fixes #2619

* Revert "fix for issue 3067"

This reverts commit 041b4b6.

Fixes #3143. The original issue (#3067) was people trying to use
tts.tts_with_vc_to_file() with XTTS and was "fixed" in #3109. But XTTS has
integrated VC and you can just do tts.tts_to_file(..., speaker_wav="..."), there
is no point in passing it through FreeVC afterwards. So, reverting this commit
because it breaks tts.tts_with_vc_to_file() for any model that doesn't have
integrated VC, i.e. all models this method is meant for.

* fix: support multi-speaker models in tts_with_vc/tts_with_vc_to_file

* fix: only compute spk embeddings for models that support it

Fixes #1440. Passing a `speaker_wav` argument to regular Vits models failed
because they don't support voice cloning. Now that argument is simply ignored.

… `model_path` (#3273)

* load multilingual model by path

* use config to assert multi lingual or not

* Moved Dockerfile, COPY at the end

This change should prevent re-installation of the dependencies upon
every change of the repository's contents. Typically if Docker detects
that something changed in a layer, all downstream layers are invalidated
and rebuilt.

* Moved Dockerfile back to main directory

Main dockerfile in a separate directory can cause issues with the
current CI/CD setup. This can be a good change for later.

* Introduced Dockerfile.dev, updated CONTRIBUTING

Dockerfile.dev can be used as a separate development environment for
anyone that does not wish to install the dependencies locally.