Feature/inverted slider 2025

[ccric]

Changed slider value calculation to allow inverting the slider by switching minimum and maximum boundaries.
Closes #4705

[FloVanGH]

Thank you very much for the PR. Three additional things:

The adjustment for the qt style is missing. For that you should check slider.rs. If you need helps just let me know.

The intention is if minimum > maximum then the slider is also drawn inverted, right? I checked your branch with the cosmic style and there the slider wasn't drawn inverted.

Could you add an example to the gallery controls_page.slint, please.

[ccric]

My initial intention was to invert the values, but that makes more sense together with also inverting the drawing.
I added that to the cosmic, cupertino, fluent and material style. The material style has some bug when drawing the sliders vertical, but that doesn't seem to be related with my changes.
I added some variants of the slider to the gallery example.

For the qt-backend: I changed the min/max boundary of the value. But I have not figured out how to render the inverted slider correct, yet.