Temporal.Time.prototype.difference should not exceed PT12H

[gibson042]

difference methods return the absolute difference between the receiver and the argument, regardless of how they compare with each other. And since time of day is modular, such comparison isn't even possible without an attached day (e.g., 10:00 is earlier than 23:00 on the same day, but later than 23:00 on the preceding day). Inferring same-day semantics makes sense for compare, but seems wrong for difference—why should 10:00 vs. 23:00 get reported as PT13H while the equal span 11:00 vs. 00:00 gets reported as PT11H? In general, why should output values greater than PT12H be possible output only when one input value happens to be in the first half of a day?

Consistent comparison-ignoring results from difference should include proper modular arithmetic for Temporal.Time values, in which no two values can be separated by more than 12 hours.