Determine missing coverage in Temporal.Calendar.p.dateAdd

[rwaldron]

[jugglinmike]

This issue was created following the initial implementation of the tests in gh-3048. The discussion in that pull request has additional information about the kinds of tests we need to improve coverage. There, @FrankYFTang volunteered to complete this work. (GitHub prevents us from formally assigning this issue to them, but the information in the tracking issue for the Temporal tests documents the assignment.)