add isPartialFormatterEnabled check for PhoneNumberTextField

[hongxinhope]

I want to disable and enable PhoneNumberTextField's parsing and changeCharacters behavior frequently, how can I do this?

I connot do this with delegate check:

// allow delegate to intervene
        guard _delegate?.textField?(textField, shouldChangeCharactersIn: range, replacementString: string) ?? true else {
            return false
        }

Can you accept this pull request， or any other way to do that?

[marmelroy]

Thanks @hongxinhope and sorry for the delay. Merged.