backends/cursor: Move out Xcursor functionality into own type

Introduce a new type MetaCursorSpriteXcursor that is a MetaCursorSprite
implementation backed by Xcursor images. A plain MetaCursorSprite can
still be created "bare bone", but must be manually provided with a
texture. These usages will eventually be wrapped into new
MetaCursorSprite types while turning MetaCursorSprite into an abstract
type.

https://gitlab.gnome.org/GNOME/mutter/issues/77

src/backends/meta-cursor-sprite-xcursor.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2013, 2018 Red Hat, Inc.
+ *
+ * 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, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef META_CURSOR_SPRITE_XCURSOR_H
+#define META_CURSOR_SPRITE_XCURSOR_H
+
+#include <glib-object.h>
+
+#include "backends/meta-cursor.h"
+
+#define META_TYPE_CURSOR_SPRITE_XCURSOR meta_cursor_sprite_xcursor_get_type ()
+G_DECLARE_FINAL_TYPE (MetaCursorSpriteXcursor, meta_cursor_sprite_xcursor,
+                      META, CURSOR_SPRITE_XCURSOR, MetaCursorSprite)
+
+MetaCursorSpriteXcursor * meta_cursor_sprite_xcursor_new (MetaCursor cursor);
+
+void meta_cursor_sprite_xcursor_set_theme_scale (MetaCursorSpriteXcursor *sprite_xcursor,
+                                                 int                      scale);
+
+MetaCursor meta_cursor_sprite_xcursor_get_cursor (MetaCursorSpriteXcursor *sprite_xcusror);
+
+Cursor meta_create_x_cursor (Display    *xdisplay,
+                             MetaCursor  cursor);
+
+#endif /* META_CURSOR_SPRITE_XCURSOR_H */