Allow scheduling events in another timezone

### Problem

As someone who lives on the opposite of the globe from most of western countries with whom I communicate, I find I often have to keep timezones in mind when scheduling events. It'd be helpful if Calendar could help me with this in the process of manually adding events to the calendar.

### Proposal

I propose a dropdown be added in the main event-editting tab for selecting a timezone, defaulting to the local timezone. Dates & times entered would be interpreted according to the selected timezone, & converted before being displayed in the calendar view.

When a timezone other than the local one is selected I'd appreciate some text being added to the UI communicating what time that is in the local timezone.

### Prior Art (Optional)

_No response_