Improve test coverage for built-in function options

[catamorphism]

https://github.com/unicode-org/message-format-wg/blob/main/spec/registry.md lists many options for the built-in :number and :datetime functions. Eventually, spec tests should be added that at least cover each options, as well as some notable combinations of options (e.g. incompatible combinations of options). At this moment, only the minimumFractionDigits option for :number has tests, and most of the field options for :datetime don't have tests.

[catamorphism]

I'm not sure whether this belongs in LDML45 or LDML46. It's unlikely to be finished for 45, but adding more tests in 45 wouldn't break anything as long as they're consistent with the existing spec.

[aphillips]

If we can do more tests for 45, great, but I'm fairly sure we won't get complete coverage in the days remaining. We should strive for that early in the Tech Preview phase. Once we have closed the book on 45, we'll probably do cadence releases during tech preview for things like this. So I'm going to tag this 46 but if you have tests, make a PR for 45.

[catamorphism]

I don't have tests yet, JFYI. I figured this would probably be a 46 thing.