Make limits and ranges work better with Calendar event queries

Summary:
Fixes T8911. This corrects several issues which could crop up if a calendar event query matched more results than the query limit:

• The desired order was not applied by the SearchEngine -- it applies the first builtin order instead. Provide a proper builtin order.
• When we generate ghosts, we can't do limiting in the database because we may select and then immediately discard a large number of parent events which are outside of the query range.
  • For now, just don't limit results to get the behavior correct.
  • This may need to be refined eventually to improve performance.
• When trimming events, we could trim parents and fail to generate ghosts from them. Separate parent events out first.
• Try to simplify some logic.

Test Plan: An "Upcoming" dashboard panel with limit 10 and the main Calendar "Upcoming Events" UI now show the same results.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T8911

Differential Revision: https://secure.phabricator.com/D16289