Today there are multiple fields in the API document referring to test ids. These fields are named either "test_id", "id" or "hash_id".

1. Choose a name to be given to all those fields.
2. Add replacement parameters with the new name for all those fields that don't already have the chosen name.
3. For each parameter that's gotten such a replacement, deprecate that parameter with a message encouraging migration to the replacement parameter.
4. Submitting both the old and new parameters together in the same request should probably be forbidden.

This should not be implemented before #790.