Schema inspection ignores types wrapped by Optional

[bclozel]

When a @Controller declares a handler method return type like Optional<Book>, the SchemaMappingInspector does not inspect the Book type and the resulting inspection report can mention the type and its fields as unmapped:

Unmapped fields: {Book=[id, title]}

The SchemaMappingInspector is currently aware of reactive types and unwraps them. We should have a similar approach for java.util.Optional.