Respect user's time formatting

Current behavior in Element is to display the timestamps on messages in 24-hour time regardless of the user's phone settings. The app should instead follow the user's time formatting settings (whether they use 24-hour or 12-hour time).

No files, tests, or entry points are named. Trace where message timestamps are rendered and how the iOS device's 12-hour or 24-hour preference is read; the work is done when message timestamps follow that preference in both formats and the relevant behavior is covered by tests.

Written by the indexing model from the issue text.