Feature Request: Support for button chords in shortcuts

Is your feature request related to a problem? Please describe.

I have a standalone scroll dial, its wonderful for adjusting settings in combination with a numpad. I get to preview the changes in fullscreen, without my eyes ever leaving the image to look at the UI.

For now, i have setup a kmonad script that maps button chords on my numpad to function keys, to increase the amount of settings i have available at my fingertips.

However, I'm running out of function keys that darktable recognizes, and kmonad scripting is quite cumbersome compared to just pressing two buttons and scrolling on the slider i would like to control.

Describe the solution you'd like

I believe button chord shortcuts would be a great value add to darktable.

It would greatly expand the amount of shortcuts reachable with one hand on the homerow, or on a numpad, and the other on the mouse.

It could also allow for shortcut mapping with "human logic", like:

c + scroll = Local contrast > details,
c + h + scroll = Lc > highlights,
c + s + scroll = Lc > shadows

should one want to do that.

Additional context

There is probably a lot of more pressing matters for you guys, but i just wanted to air the interest, should some of you find yourself in a situation where implementing such a function wouldn't be too complicated.

I really love darktable, and I'm really grateful for all the work you guys are doing. Maybe in the future, when my coding skills are more to write home about, I'll come and try to help out!

The issue names no files, tests, or entry points. Start by locating darktable's existing shortcut handling and clarifying how button chords, scrolling, conflicts, timing, and mappings should work; done would require agreed behavior and tests covering the proposed chord examples.