Make descriptions unique

Recently, there was some discussion on whether test case descriptions should be unique: https://github.com/exercism/problem-specifications/pull/2019#discussion_r855117856
IMO there is an unwritten rule that each description _should_ be unique, but it is not documented anywhere I think.
To me, it seems like having unique descriptions is useful for several reasons:

- It makes for easier identification of test cases (descriptions are easier to scan than UUIDs)
- It is often a prerequisite for test generators that a (full) description is unique

To be clear, when I'm referring to a description being unique, what I mean is that the _concatenated description_ of a test case must be unique. In other words, the uniqueness also takes into account any description of parent test case goupings.

@wolf99 Would something like this be possible to encode in the JSON schema we have?