smtr: Structs have local scope

Also unique_name can take field_name directly.

backends/functional/smtlib_rosette.cc

@@ -75,15 +75,16 @@ class SmtrStruct {
 	};
 	idict<IdString> field_names;
 	vector<Field> fields;
-	SmtrScope &scope;
+	SmtrScope &global_scope;
+	SmtrScope local_scope;
 public:
 	std::string name;
-	SmtrStruct(std::string name, SmtrScope &scope) : scope(scope), name(name) {}
+	SmtrStruct(std::string name, SmtrScope &scope) : global_scope(scope), local_scope(), name(name) {}
 	void insert(IdString field_name, SmtrSort sort) {
 		field_names(field_name);
-		auto base_name = scope.unique_name("\\" + RTLIL::unescape_id(field_name));
+		auto base_name = local_scope.unique_name(field_name);
 		auto accessor = name + "-" + base_name;
-		scope.reserve(accessor);
+		global_scope.reserve(accessor);
 		fields.emplace_back(Field{sort, accessor, base_name});
 	}
 	void write_definition(SExprWriter &w) {