This changes how state is tracked by introducing an explicit state. We
need this since we use asynchronous calls to the out of process
component that handles actual inhibitation, including idleness.
This means if inhibitations changes rapidly, we might end up with an
incorrect state if we e.g. try to uninhibit while we're currently trying
to inhibit.
This is done by adding a state variable that accounts for the pending
state, as well as the active state, with a function that looks at the
current conditions to derive what state we should be in, and what state
we are in, to decide what the next action should be.
For example, if we're trying to inhibit, but now wants to uninhibit,
we'll wait for the inhibit call to complete, recheck what we want, which
would result in an async uninhibit call being made.
Fixes: 388b534062 ("wayland: Implement idle inhibit protocol")
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3219>
