feat(developer): emit ldml test case as markdown 🙀

Given LDML test format:
```xml















```

... we could have a tool convert this into markdown so users can run the test manually, something like:

> ## Test: key-8
> press 8
> Check that the result is 8:ctxt:OK
>
> ## Test: key-8-osage
> 1. copy this string: `𐓏`
> 2. press 8
> 3. Check that the result is 8:ctxt:ok

This could be used to (for example) maintain a TESTING.md automatically in the https://github.com/keyman-keyboards/ldml_test repo, generated from the unit test xml.

related to #10192 and #10505