Support for signing into Matrix accounts backed by single-sign-on

As part of Fedora's transition of real-time chat from primarily IRC to primarily Matrix, we would like to ship NeoChat to easily allow people to use the Fedora Matrix server.

However, Fedora's Matrix server (chat.fedoraproject.org, which is not yet online), will use Single-Sign-On using OpenID Connect through id.fedoraproject.org. As far as I'm aware, only Element supports SSO-backed Matrix account login, and it's quite important that NeoChat would too.