Add detectPlatform to always use wayland in a wayland session
Summary:
It's possible that Qt uses the xcb platform by default even in a Wayland
session, so detect such cases and switch to wayland instead to enable
proper support for remote input. Copy code from libkworkspace to not
introduce a dependency.
Test Plan: Started kdeconnectd, uses wayland platform now. Remote input works.
Reviewers: KDE Connect, nicolasfella
Reviewed By: KDE Connect, nicolasfella
Subscribers: kdeconnect
Tags: KDE Connect
Differential Revision: https://phabricator.kde.org/D22562