USD: Enable operator presets when exporting

This patch enables operator presets for USD exports.
The export menu has many options, so enabling the feature
will help users manage their export settings in the same
way they can with other filetypes.

Same as {rB1d668b635632}

Differential Revision: https://developer.blender.org/D14896

source/blender/editors/io/io_usd.c

@@ -217,6 +217,7 @@ void WM_OT_usd_export(struct wmOperatorType *ot)
   ot->check = wm_usd_export_check;
 
   ot->flag = OPTYPE_REGISTER; /* No UNDO possible. */
+  ot->flag |= OPTYPE_PRESET;
 
   WM_operator_properties_filesel(ot,
                                  FILE_TYPE_FOLDER | FILE_TYPE_USD,