This updates the MF2 spec tests to 943479b602 with the following exceptions:
- functions/currency.json and functions/math.json are omitted because these are not yet implemented
- bidi.json will be handled in a future PR
- u-options.json will be handled in a future PR
Changes include:
* `:integer` now returns a value encapsulating the rounded numeric value of the argument, rather than
the value itself.
* Fallbacks are handled according to the current spec.
* Fallback values are not passed into functions.
* Characters inside literal fallbacks are properly escaped.
* The test runner skips null values properly.
* The test runner handles boolean `expErrors` in defaultTestProperties.
* `:string` normalizes its input and normalizeNFC() has been refactored so it can be called there.
