build_schema: change implementation to simply extending empty schema

Replicates graphql/graphql-js@3948aa2

Author: Cito

src/graphql/type/schema.py

@@ -226,9 +226,7 @@ def to_kwargs(self) -> Dict[str, Any]:
             mutation=self.mutation_type,
             subscription=self.subscription_type,
             types=FrozenList(self.type_map.values()) or None,
-            directives=None
-            if self.directives is specified_directives
-            else self.directives,
+            directives=self.directives[:],
             extensions=self.extensions,
             ast_node=self.ast_node,
             extension_ast_nodes=self.extension_ast_nodes,

src/graphql/utilities/__init__.py

@@ -20,10 +20,10 @@
 from .build_client_schema import build_client_schema
 
 # Build a GraphQLSchema from GraphQL Schema language.
-from .build_ast_schema import build_ast_schema, build_schema, get_description
+from .build_ast_schema import build_ast_schema, build_schema
 
 # Extend an existing GraphQLSchema from a parsed GraphQL Schema language AST.
-from .extend_schema import extend_schema
+from .extend_schema import extend_schema, get_description
 
 # Sort a GraphQLSchema.
 from .lexicographic_sort_schema import lexicographic_sort_schema