Now that there are two things that snap (blocks and WS comments), the alignment code in being moved to a common place.

Co-authored-by: Christopher Allen <cpcallen+git@google.com>

Co-authored-by: Christopher Allen <cpcallen+git@google.com>

The point of null was to avoid creating a new coordinate object and avoid a more complicated check.  But this can also be achieved by returning the original input coordinate object.