Implementing interfaces can introduce warnings in other libraries

```csharp
interface I {
void M();
}

class Base {
[RUC("RUC")]
public virtual void M() {}
}

class Derived : Base, I {
}
```

Here, the base class and interface are unrelated until `Derived` implements the interface via the base method:

`ILLink : Trim analysis warning IL2046: Base.M(): Member 'Base.M()' with 'RequiresUnreferencedCodeAttribute' implements interface member 'I.M()' without 'RequiresUnreferencedCodeAttribute'. 'RequiresUnreferencedCodeAttribute' annotations must match across all interface implementations or overrides.`

The warning should point to `Derived` since it is responsible for introducing the link between the base/interface methods. Otherwise this allows one library to introduce trim analysis warnings in a different library that is already annotated.