[llvm] [TableGen] Rework error reporting for duplicate Feature/Processor. (PR #102257)

[Rahul Joshi via llvm-commits]

jurahul wrote:

I realized that I forgot to update the commit message to describe the getID() changes :( It has:

```
    - Make the sorting deterministic by using record name as a secondary
      key for sorting, and re-enable SubtargetFeatureUniqueNames.td test
      that was disabled due to the non-determinism of the error messages.
    - Change wording of error message when duplicate records are found to
      be source code position agnostic, since `First` may not be before
      `Second` lexically.
```

Oh well, need to be more careful next time.

https://github.com/llvm/llvm-project/pull/102257