Resizing pattern at the start

Whether expect implement a resize of pattern at the start and not only at the end as now. The lack of this feature makes working with patterns in LMMS extremely uncomfortable :-(

No files, tests, or entry points are named in the issue. Locate the existing pattern-resizing implementation, determine how it currently handles resizing at the end, and define the corresponding behavior for resizing at the start; done means patterns can be resized from their beginning without disrupting existing editing behavior.

Written by the indexing model from the issue text.