R1:0ce7eacaf1c1

Introduce Calendar "UTC Epoch" columns for query windowing

Summary:
Ref T10747. Currently, Calendar events are mostly epoch-based and cheat a little bit for all-day events.

This already felt a little flimsy, and can't reasonably accommodate the full range of `.ics` events, which include "floating" events (e.g., occurs at 3PM regardless of timezone, like "Tea Time").

As a secondary issue, we identify instances of a recurring event by instance number (1, 2, 3, etc.). This can't accommodate the full range…