Comment 0 for bug 1388987

In include/common/mir_toolkit/cursors.h, there are cursor names mir_diagonal_resize_bottom_to_top_cursor_name and mir_diagonal_resize_top_to_bottom_cursor_name, but these can't be used for the top-left and bottom-left icons since they aren't diagonally symmetrical. We need four different names for the four different possible directions.