Merge branch 'jt/commit-graph-per-object-store'

The singleton commit-graph in-core instance is made per in-core
repository instance.

* jt/commit-graph-per-object-store:
  commit-graph: add repo arg to graph readers
  commit-graph: store graph in struct object_store
  commit-graph: add free_commit_graph
  commit-graph: add missing forward declaration
  object-store: add missing include
  commit-graph: refactor preparing commit graph

ref-filter.c

@@ -1713,7 +1713,7 @@ static enum contains_result contains_tag_algo(struct commit *candidate,
 
 	for (p = want; p; p = p->next) {
 		struct commit *c = p->item;
-		load_commit_graph_info(c);
+		load_commit_graph_info(the_repository, c);
 		if (c->generation < cutoff)
 			cutoff = c->generation;
 	}