Collect variables, components, form fields etc. from all classes implementing some interface

[lulco]

Example:

private AddFieldsToFormInterface $addFieldsToForm;
...
$form = new Form();
$this->addFieldsToForm->addFields($form);

AddFieldsToFormInterface can have several implementations, we need to collect data from all of them.

Then we should merge them - if variable is collected from all implementations, it is always defined, if it is only in some implementations, it is optional (might not be defined).

I believe this is already collected, we just need to return it from Finder classes