lib/ref: Add OstreeCollectionRef type for globally unique refs

This is a type representing the tuple (collection ID, ref name), which is
guaranteed to be globally unique. It will be used in upcoming commits.

It introduces the concept of a ‘collection’ which is a unique, curated
set of refs which lie in the same trust domain (i.e. all signed by the
same key and validated by the same developer). Flathub might be a
collection, for example; or the set of OS refs coming from a particular
OS vendor.

It includes a function for validating collection IDs.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #924
Approved by: cgwalters

src/libostree/ostree-core-private.h

@@ -173,6 +173,15 @@ _ostree_raw_file_to_archive_stream (GInputStream       *input,
                                     GCancellable       *cancellable,
                                     GError            **error);
 
+#ifndef OSTREE_ENABLE_EXPERIMENTAL_API
+gboolean ostree_validate_collection_id (const char *collection_id, GError **error);
+#endif /* !OSTREE_ENABLE_EXPERIMENTAL_API */
 
+#if (defined(OSTREE_COMPILATION) || GLIB_CHECK_VERSION(2, 44, 0)) && !defined(OSTREE_ENABLE_EXPERIMENTAL_API)
+#include <libglnx.h>
+#include "ostree-ref.h"
+G_DEFINE_AUTOPTR_CLEANUP_FUNC (OstreeCollectionRef, ostree_collection_ref_free)
+G_DEFINE_AUTO_CLEANUP_FREE_FUNC (OstreeCollectionRefv, ostree_collection_ref_freev, NULL)
+#endif
 
 G_END_DECLS