[ty] Include definition site for "members of" API

In the course of writing the "add an import" implementation,
I realized that we needed to know which symbols were in scope
and how they were defined. This was necessary to be able to
determine how to add a new import in a way that (minimally)
does not conflict with existing symbols.

I'm not sure that this is fully correct (especially for
symbol bindings) and it's unclear to me in which cases a
definition site will be missing. But this seems to work for
some of the basic cases that I tried.

crates/ty_python_semantic/src/semantic_model.rs

@@ -236,9 +236,9 @@ impl<'db> SemanticModel<'db> {
         for (file_scope, _) in index.ancestor_scopes(file_scope) {
             completions.extend(
                 all_declarations_and_bindings(self.db, file_scope.to_scope_id(self.db, self.file))
-                    .map(|member| Completion {
-                        name: member.name,
-                        ty: Some(member.ty),
+                    .map(|memberdef| Completion {
+                        name: memberdef.member.name,
+                        ty: Some(memberdef.member.ty),
                         kind: None,
                         builtin: false,
                     }),