Set #maxlength for TelephoneDefaultWidget to the one specified in TelephoneItem plugin

Problem/Motivation

We hardcoded length for TelephoneItem to 256. However TelephoneDefaultWidget doesn't set #maxlength in TelephoneDefaultWidget::formElement() which makes it be set to 128 (default for Drupal\Core\Render\Element\Tel).

Steps to reproduce

1. Add a telephone field to a content type
2. Inspect the field and verify maxlengh is 128

Proposed resolution

Set TelephoneDefaultWidget maxlength to 256

Remaining tasks

Code review
Commit

User interface changes

NA

API changes

NA

Data model changes

NA

Release notes snippet

NA

Screenshots

Before patch (via #44)

After patch (via #44)