Enhance Slider -> LinearRange with better styling

[tig]

I had hopes for Slider.

Don't get me wrong, I like this View. It does a lot of things great.

However, it's not the Slider I envisioned. I want this:

I could continue to tweak the existing Slider to have modes like the above. But that's just complex.

Instead, I want to write a new View based on ScrollSlider in

• Fixes #2489. New ScrollSlider and ScrollBar - Any View can have scrollbars easily #3820

Anyone object to me renaming the existing Slider to something that better describes it as I do this?

• RangeSlider?
• MultiSlider?

???

[tig]

After digging in, I've changed my mind.

Slider can work for what I want. But I am going to rename it: LinearRange as that's what other frameworks call similar controls these days.