Merge branch 'ps/worktree-refdb-initialization'

Instead of manually creating refs/ hierarchy on disk upon a
creation of a secondary worktree, which is only usable via the
files backend, use the refs API to populate it.

* ps/worktree-refdb-initialization:
  builtin/worktree: create refdb via ref backend
  worktree: expose interface to look up worktree by name
  builtin/worktree: move setup of commondir file earlier
  refs/files: skip creation of "refs/{heads,tags}" for worktrees
  setup: move creation of "refs/" into the files backend
  refs: prepare `refs_init_db()` for initializing worktree refs

worktree.c

@@ -12,18 +12,23 @@
 #include "wt-status.h"
 #include "config.h"
 
+void free_worktree(struct worktree *worktree)
+{
+	if (!worktree)
+		return;
+	free(worktree->path);
+	free(worktree->id);
+	free(worktree->head_ref);
+	free(worktree->lock_reason);
+	free(worktree->prune_reason);
+	free(worktree);
+}
+
 void free_worktrees(struct worktree **worktrees)
 {
 	int i = 0;
-
-	for (i = 0; worktrees[i]; i++) {
-		free(worktrees[i]->path);
-		free(worktrees[i]->id);
-		free(worktrees[i]->head_ref);
-		free(worktrees[i]->lock_reason);
-		free(worktrees[i]->prune_reason);
-		free(worktrees[i]);
-	}
+	for (i = 0; worktrees[i]; i++)
+		free_worktree(worktrees[i]);
 	free (worktrees);
 }
 
@@ -75,8 +80,8 @@ static struct worktree *get_main_worktree(int skip_reading_head)
 	return worktree;
 }
 
-static struct worktree *get_linked_worktree(const char *id,
-					    int skip_reading_head)
+struct worktree *get_linked_worktree(const char *id,
+				     int skip_reading_head)
 {
 	struct worktree *worktree = NULL;
 	struct strbuf path = STRBUF_INIT;