[clang] [clang] [diagnostics] Stable IDs for Clang diagnostics (PR #168153)

[Erich Keane via cfe-commits]

erichkeane wrote:

> Separate bikeshed thread on what the right name for `OldStableIds` is:
> 
>     1. `OldStableIds` - Pro: Short. Con: Not very clear what it means.
> 
>     2. `DeprecatedStableIds` - Pro: Matches the SARIF property name. Cons: Longer, still not super clear (but probably more clear than `OldStableIds`).
> 
>     3. `PreviousStableIds` - Pro: Slightly more clear, YMMV.
> 
>     4. Other suggestions?
> 
> 
> My preference: Either `DeprecatedStableIds` or `PreviousStableIds`.

`LegacyStableIds`?  Whichever we do is going to need extensive documentation, so I don't have a strong preference.  `Previous` strikes me the 'least', and `Old` is kinda bad.  `Deprecated` has the advantage of actually being what is in SARIF, so I think I'm between `Legacy` and `Deprecated`, but I'm a touch of a coin-flip.

https://github.com/llvm/llvm-project/pull/168153