Filter out disabled clients in the autostart login process

Problem/Motivation

The current behaviour of the OpenID Connect module does not handle the filtering of disabled clients effectively when trying to determine if only one OpenID Connect client is active.

Steps to reproduce

1. Enable the OpenID Connect module.
2. Set more than one client and disable one or more of them, but ensure that only one client is enabled.
3. Enable the Autostart login process setting in the OpenID Connect settings at /admin/config/people/openid-connect/settings.
4. Attempt to authenticate by visiting the /user/login page to trigger the auto-login.
5. Expect the auto-start login to occur, but instead, the Drupal login form will be shown.

Proposed resolution

This patch modifies the OpenID Connect auto-login logic to filter out disabled clients before evaluating whether only one client is enabled.

Remaining tasks

TBD

User interface changes

N/A

API changes

N/A

Data model changes

N/A