revert removal of url import

Revert change made in #2293, the router uses deno for the router-bridge, and url is not built in (#2451)

Author: clenfest

.changeset/dirty-phones-refuse.md

@@ -0,0 +1,6 @@
+---
+"@apollo/federation-internals": patch
+---
+
+Revert #2293. Removing URL import causes a problem when running under deno.
+  

internals-js/src/coreSpec.ts

@@ -1,4 +1,5 @@
 import { ASTNode, DirectiveLocation, GraphQLError, StringValueNode } from "graphql";
+import { URL } from "url";
 import { CoreFeature, Directive, DirectiveDefinition, EnumType, ErrGraphQLAPISchemaValidationFailed, ErrGraphQLValidationFailed, InputType, ListType, NamedType, NonNullType, ScalarType, Schema, SchemaDefinition, SchemaElement, sourceASTs } from "./definitions";
 import { sameType } from "./types";
 import { assert, firstOf } from './utils';