core: Move pack file parsing into core, add ostree_create_file_from_input() API

This moves us closer to consistently passing around a triple of:
  (GFileInfo *info, GVariant *xattrs, GInputStream *content)
Which will help the libarchive work.

src/libotutil/ot-gio-utils.c

@@ -34,6 +34,19 @@
 #define O_BINARY 0
 #endif
 
+GFileType
+ot_gfile_type_for_mode (guint32 mode)
+{
+  if (S_ISREG (mode))
+    return G_FILE_TYPE_REGULAR;
+  else if (S_ISLNK (mode))
+    return G_FILE_TYPE_SYMBOLIC_LINK;
+  else if (S_ISBLK (mode) || S_ISCHR(mode) || S_ISFIFO(mode))
+    return G_FILE_TYPE_SPECIAL;
+  else
+    return G_FILE_TYPE_UNKNOWN;
+}
+
 gboolean
 ot_gfile_ensure_directory (GFile     *dir,
                            gboolean   with_parents,