Support "text" fields

Problem/Motivation

Fields provided by core module text cannot be mapped.

Steps to reproduce

Configure opoenid_connect to map an SSO property to a user field of type "text".

When connecting with a user with such a configuration, following errors appear in the logs:

Could not save user info, property type not implemented: text

Which is an error logged in \Drupal\openid_connect\OpenIDConnect::saveUserinfo()

Proposed resolution

Add "text" as a supported data type.