[python-package] add validate_features argument to refit

[jmoralez]

Builds on #4909 adding the validate_features argument to the Booster.refit method.

[jameslamb]

nice, thank you!

[StrikerRUS]

LGTM!

[StrikerRUS]

What do you think about this predict() call?

LightGBM/python-package/lightgbm/basic.py

Lines 1402 to 1404 in ab9236b

	init_score = predictor.predict(data,
	raw_score=True,
	data_has_header=data_has_header)

Do we need validate_features param there?

[jmoralez]

We could try to add it to _set_init_score_by_predictor but it has to go through a lot of places, I'm not sure if it's worth it. WDYT?

[StrikerRUS]

OK, let's not add it into the Dataset constructor.

[github-actions]

This pull request has been automatically locked since there has not been any recent activity since it was closed. To start a new related discussion, open a new issue at https://github.com/microsoft/LightGBM/issues including a reference to this.