Currently, events default to "private events", effectively: they are visible to the host and invitees.
I think we have enough distinct types of events to present a modal option prior to event creation. Basically, turn "Create Event" into a dropdown:
> Create Private Event
> Create Public Event
> Schedule Meeting (T8022)
> Create Recurring Event (T2896)
For "Public", the only difference for now is that "Visible To" defaults to "getMostOpenPolicy()".
For "Schedule Meeting", we'd set the `isFluid` flag and switch to constraint-based scheduling (T8022).
For "Recurring Event", we'd use an alternate UI we eventually build in T2896.