Issue #9994: do not call g_file_info_get_is_hidden() (and others) directly.

This is not the main reason for the specific output in #9994. These ones are
more probably because of similar usage in GTK (which updated its own calls to
g_file_info_get_is_hidden|backup() in version 3.24.38). But we should likely
also update the various calls we have to use the generic
g_file_info_get_attribute_*() variants.

To be fair, it is unclear to me when we can be sure that an attribute is set.
For instance, when we call g_file_enumerate_children() or g_file_query_info()
with specific attributes, docs say that it is still possible for these
attributes to not be set. So I assume it means we should never use direct
accessor functions.

The only exception is that I didn't remove usage of g_file_info_get_name(),
since its docs says:

> * Gets a display name for a file. This is guaranteed to always be set.

Even though it also says just after:

> * It is an error to call this if the #GFileInfo does not contain
> * %G_FILE_ATTRIBUTE_STANDARD_DISPLAY_NAME.

Which is very contradictory. But assuming that this error warning was
over-zealous documentation, I kept the direct accessors since they are supposed
to be slightly more optimized (still according to in-code documentation) so
let's priorize them when we know they are set for sure.

plug-ins/script-fu/libscriptfu/script-fu-scripts.c

@@ -316,11 +316,11 @@ script_fu_load_directory (GFile *directory)
 
       while ((info = g_file_enumerator_next_file (enumerator, NULL, NULL)))
         {
-          GFileType file_type = g_file_info_get_file_type (info);
+          GFileType file_type = g_file_info_get_attribute_uint32 (info, G_FILE_ATTRIBUTE_STANDARD_TYPE);
 
           if ((file_type == G_FILE_TYPE_REGULAR ||
                file_type == G_FILE_TYPE_DIRECTORY) &&
-              ! g_file_info_get_is_hidden (info))
+              ! g_file_info_get_attribute_boolean (info, G_FILE_ATTRIBUTE_STANDARD_IS_HIDDEN))
             {
               GFile *child = g_file_enumerator_get_child (enumerator, info);