Support evaluationDateTime as a parameter in the tests

[brynrhodes]

Some of the tests reference the Today(), Now(), and TimeOfDay() functions. According to the spec, these functions are expected to return a result based on the "evaluation request date time", we should add that value as an attribute of the tests.

[evan-gordon]

Adding a comment here based on our Zulip chat discussion

DateTimeToString2 is another case where the outputs of this test rely on the evaluation request date time.