Enable adaptive step size for tone frequency and GOP

[HaraldNordgren]

I created this functionality within Qt itself a few years back, see documentation here: https://doc.qt.io/qt-6/qspinbox.html#setStepType

It's already used by qBittorrent for its upload and download limits: qbittorrent/qBittorrent#21138. Maybe it can be useful here too?

[bmatherly]

Can you explain why you picked the encode GOP and the tone frequency? Are those two controls special that they benefit from this mode? Or did you just choose them as examples?

We use spin boxes all over the place in Shotcut - both the QSpinBox and the QML version in our filter controls. In general, I think we would want consistent behavior across the application so that users are not surprised if some act differently. But maybe there is a good reason for some spinboxes to have special behaviors.

[ddennedy]

I think we would want consistent behavior

Step size per control, which is a good thing we are using, is inherently inconsistent. I do not think this makes sense for GOP, though. A step size other than 1 should be base on time, such as 1 second depending upon frame rate, instead of an arbitrary 10 frames, which is what this will be most of the time. Can be frustrating to try to get to a particular number, going up and down, only to settle for typing it.

[HaraldNordgren]

Can you explain why you picked the encode GOP and the tone frequency? Are those two controls special that they benefit from this mode? Or did you just choose them as examples?

Yes, the were chosen without much regard because I thought they made sense (but maybe GOP doesn't based on @ddennedy's comment).

I didn't want to change all boxes as the first step. But I'm very open to suggestions!