[Slider] Add mention that `onMouseDown`/`onMouseUp` aren't functional

[benoitgrelard]

Suggest onPointerDown/onPointerUp instead.

Hi @benoitgrelard, maybe worth mentioning in the doc? I think onMouseDown and onMouseUp are pretty commonly used events.

Originally posted by @Bailig in https://github.com/radix-ui/primitives/issues/1640#issuecomment-1238047368

[ItzaMi]

@benoitgrelard , is this something that I could work on? Would adding a Caveats section with this info be enough?

[benoitgrelard]

Happy for you to kickstart a PR and we can go from there!

[abyadando]

@benoitgrelard I can see it's still open, so I've decided to take care of it.