BUG ArrayList failing to respect the SS_Sortable interface

According to SS_Sortable::sort it should be perfectly fine to add sort expressions in 'Name DESC' format.
In many places it's necessary to quote the sort column (e.g. GridFieldSortableHeader) meaning that ArrayList cannot be used as a sortable GridField source, so the parser has been extended to consider this.
Tests extended to demonstrate possible use cases.

Previously, ArrayList would either throw an error or silently ignore the sorted column.

ref: CWPBUG-133