Implement interface extension

This solves some issues where types couldn't be reconciled because they
implemented multiple interfaces. The PR for this in the GraphQL PHP
project is now far enough along (all tests passing) that this should be
available in an update for us in time.

See: webonyx/graphql-php/pull/740

Author: Kingdutch

modules/custom/social_graphql/graphql/open_social.graphqls

@@ -197,10 +197,7 @@ type DateTime {
 """
 Media managed by the Open Social platform.
 """
-# Unfortunately webonyx/graphql-php does not yet support interfaces implementing
-# other interfaces which was added to v15 of the GraphQL.
-# See https://github.com/webonyx/graphql-php/issues/728.
-interface Media { #}implements NodeInterface {
+interface Media implements Node {
   uuid: ID!
   """
   The url at which the original media can be downloaded.