[clang] Add support for referencable labels for attribute documentation (PR #118428)

[Aaron Ballman via cfe-commits]

================
@@ -55,6 +55,9 @@ class Documentation {
   // When set, specifies that the attribute is deprecated and can optionally
   // specify a replacement attribute.
   DocDeprecated Deprecated;
+
+  // When set, specifies a label that can be used to reference the documentation
----------------
AaronBallman wrote:

```suggestion
  // When set, specifies a label that can be used to reference the documentation.
```

https://github.com/llvm/llvm-project/pull/118428