Rename testdata.yaml to test_group.yaml and implement Test Case Configuration

[mpsijm]

This PR renames testdata.yaml to test_group.yaml (as defined here) and introduces Test Case Configuration .yaml files (as defined here).
Additionally, .hint and .desc files are no longer used: they should now be keys (hint: and description:, respectively) in the Test Case Configuration file.

A lot has changed, and I think everything still works, but please verify 😇 bt upgrade should also properly take care of both migrations, both in data/ and in generators.yaml.

A special request for @thorehusfeldt if you have the time (if not, also fine 🙂): can you double-check the schemas for test_group.yaml and <testcase>.yaml with the latest version of the spec? 😄

[mzuenni]

Looks good to me just added 3 remarks

[mpsijm]

Thanks for the comments, I fixed them 😄

[mzuenni]

Everything looks good to me :)

[mpsijm]

Okay, I've finally found some time to verify that the updated generators_yaml_schema.json works properly in my editor 😄 Turns out it was as simple as adding this line at the top of some generators.yaml file (only works if your editor actually uses yaml-language-server under the hood):

# yaml-language-server: $schema=file:///home/maarten/git/contest/BAPCtools/support/schemas/generators_yaml_schema.json

I've even found and fixed a little bug that has been in the schema for a while already 😛

Regarding the Cue schemata: we have a CI test script (test/yaml/generators/test_schemata.sh) that runs cue vet on a bunch of generators.yaml files, so I assume that'll be all right 😄