[clang] [analyzer] Report violations of the "returns_nonnull" attribute (PR #106048)

[Donát Nagy via cfe-commits]

================
@@ -588,8 +588,8 @@ Warns when a null pointer is passed to a pointer which has a _Nonnull type.
 
 .. _nullability-NullReturnedFromNonnull:
 
-nullability.NullReturnedFromNonnull (ObjC)
-""""""""""""""""""""""""""""""""""""""""""
+nullability.NullReturnedFromNonnull
+"""""""""""""""""""""""""""""""""""
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NagyDonat wrote:

```suggestion
nullability.NullReturnedFromNonnull (C, C++, ObjC)
""""""""""""""""""""""""""""""""""""""""""""""""""
```
This is how other checkers are marked. (Do I understand correctly that `__attribute__((returns_nonnull))` is relevant both under C and C++?)

https://github.com/llvm/llvm-project/pull/106048