controllers: add helper to control "waveform_zoom" with potmeters

[ronso0]

This came up in the forums https://mixxx.discourse.group/t/waveform-zoom-midi-control-on-a-cc-dial/28293

• first comit is just a cleanup after I failed to find "behaviour"
• second commit is the script helper: default is a continuous range, set 'round' to true to get discrete integer steps
• third commit fixes some mappings using the waveform_zoom with the ancient range 0..6

TODO

• add note to [ChannelN],waveform_zoom, improve Feedback note
• remove 'zoom' from ControlPotmeter controls examples

[mxmilkiib]

Very nice, thank you, but, ultimately, why not push it down to the C++ level? That way it could be bound to a control via the GUI/wizard.

Maybe I'm wrong, but I'm starting to get the feeling there's a "standard library" of these kinds of level of neat functionality that aren't bindable via the UI? Which as I wordly put on #12337, is an abstraction that's beyond the scope of most users.

[daschuer]

Yes, can't we make it a ControlPotmeter?

[ronso0]

I've tried that, or rather I tried to make a helper pot.

The issue with waveform_zoom is that the user can set the default value at runtime via the waveform preferences, hence we can of course create a ControlPotmeter (and set a step size of 1 so the GUI zoom buttons still work as before) but as soon as the default is changed the _set_default CO would not be working as expected anymore.
I also looked into creating a ControlPotmeterSimple that does not create all sub-controls (only _up/_down) and keep the _set_default pushbutton separate, but that that was too much just for one control.

We could also connect the preferences combobox to a separate ControlObject waveform_zoom_set_default_value which then triggers a slot in BaseTrackPlayer to zoomCO->setDefault(newDefaultvalue). I didn't check if that is even possible after the control is created and that also felt like a bit too much work.
I can check that again though.

One thing to note: if you want individual zoom levels per deck (to look ahead or tweak cues on a deck while having the overview on another) the current stepped behaviour is good since it is very easy to manually re-sync the zoom levels of multiple decks. With a continuous range that's almost impossible.

[ronso0]

We could also connect the preferences combobox to a separate ControlObject waveform_zoom_set_default_value which then triggers a slot in BaseTrackPlayer to zoomCO->setDefault(newDefaultvalue). I didn't check if that is even possible after the control is created and that also felt like a bit too much work.

Okay, that was easier than expected.

Replaced by #12387