Slider helper.

Is your feature request related to a problem? Please describe. No, my feature request isn't related to an issue, though it is important for consistency.

Describe the solution you'd like Right now, there are many ui helpers like ui.button() and ui.label(). However, to add a slider, you need to call this: ui.add(egui::Slider::new(...));

I think it should be made consistent with the other elements which have helpers, meaning that you can call it as this: ui.slider(value, range);

Describe alternatives you've considered There is no alternative fix other than the user making a trait and function for the egui::Slider and implementing them.

Additional context Nothing else to add.