New future. Add setSize(numeratedSteps) for selected area in pianoroll.

For editing imported midi, especially for stretching notes will be very productive , have a function which allow stretching selected area of notes to predetermined size/length.
For example stretch proportionally to 18 patterns from left first note of selection start moment, to right. Long stretching uses mouse create shitty result, especially if steps of stretching, more than one. Because intermediate step displacement of notes is present.
Ideally 18 not enough. It can be expanded to internal steps too 18 7/8 etc... depend of track settings.

Start by locating the pianoroll selection and note-stretching entry points. Clarify how setSize(numeratedSteps) should map the selected range to patterns and internal step divisions, including track settings, then identify tests or reproducible MIDI cases for the expected result.

Written by the indexing model from the issue text.