This fixes the name of reported external APIs for nested types. The
`getDeclaringType().getUnboundDeclaration()`'s `toString()` method
reports the name of the type, but not the name of the declaring type.
This results in missing information in the
`UnsupportedExternalAPIs.ql` query.
For example, previously it would report:
```
GitHub.Nested#NestedClass.Test()
```
However, the `NestedClass` class does not exist in the namespace and is
only a nested type within `MyFirstClass`. The correct name should be:
```
GitHub.Nested#MyFirstClass+NestedClass.Test()
```
This name also matches the format of MaD.
6812389fc8