[autoform] Use fieldclass from kwargs in guess_field for non-final relations This follows up on af969080e7e6 in which a "fieldclass" kwarg has been added in EntityFieldsForm.field_by_name() before calling guess_field(). In this changeset, this value was only used for final relation but the way non-final relation actually also changed since we also use guess_field from these relation (previously, the field class specified through uicfg was instantiated directly in EntityFieldsForm.field_by_name()). So in the non-final case in guess_field() we simply try to retrieve "fieldclass" from kwargs and fall back to RelationField.

Release notes
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    3.25
    3.24
    3.23
    3.22
    3.21
    3.20
    3.19
    3.18
    3.17
    3.16
    3.15
    3.14