Port KIdleTime to ext_idle_notifier_v1

Effectively the same as the current protocol, but reworded:

simulateUserActivity has been completely dropped from both implementations as no-one uses it*. See https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/29

Draft as the proposal is not released yet and it has not been adequately tested against a patched kwin

*technically konversation does, but for a misguided reason that I'm about to fix. It'll just no-op if called.