Make MetaSelection, MetaSelectionSource and MetaMemorySelectionSource public

This exposes the base so that we can reimplement StClipboard on top. Some
gtk-docs have been added for documentation and introspection purposes.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/320

src/meta/meta-selection.h

@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2018 Red Hat
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ *
+ * Author: Carlos Garnacho <carlosg@gnome.org>
+ */
+
+#ifndef META_SELECTION_H
+#define META_SELECTION_H
+
+#include <gio/gio.h>
+
+#include <meta/common.h>
+#include <meta/display.h>
+#include <meta/meta-selection-source.h>
+
+#define META_TYPE_SELECTION (meta_selection_get_type ())
+
+META_EXPORT
+G_DECLARE_FINAL_TYPE (MetaSelection,
+                      meta_selection,
+                      META, SELECTION,
+                      GObject)
+
+META_EXPORT
+MetaSelection *
+         meta_selection_new                  (MetaDisplay *display);
+
+META_EXPORT
+void     meta_selection_set_owner            (MetaSelection        *selection,
+                                              MetaSelectionType     selection_type,
+                                              MetaSelectionSource  *owner);
+META_EXPORT
+void     meta_selection_unset_owner          (MetaSelection        *selection,
+                                              MetaSelectionType     selection_type,
+                                              MetaSelectionSource  *owner);
+
+META_EXPORT
+GList *  meta_selection_get_mimetypes        (MetaSelection        *selection,
+                                              MetaSelectionType     selection_type);
+
+META_EXPORT
+void     meta_selection_transfer_async       (MetaSelection        *selection,
+                                              MetaSelectionType     selection_type,
+                                              const gchar          *mimetype,
+                                              gssize                size,
+                                              GOutputStream        *output,
+                                              GCancellable         *cancellable,
+                                              GAsyncReadyCallback   callback,
+                                              gpointer              user_data);
+META_EXPORT
+gboolean meta_selection_transfer_finish      (MetaSelection        *selection,
+                                              GAsyncResult         *result,
+                                              GError              **error);
+
+#endif /* META_SELECTION_H */