[Slider] Add sx prop in SliderStyled

[mnajdova]

This PR adds the sx prop on the SliderStyled component.

Example usage:

<Slider
  defaultValue={30}
  aria-labelledby="disabled-slider"
  sx={{
    m: 2,
    color: 'secondary.main',
    bgcolor: 'primary.light',
  }}
/>

Related to #15561

[eps1lon]

I'm not really following how this prop is useful for complex components. Could you share a real-world use case?

[oliviertassinari]

Could you share a real-world use case?

@eps1lon In https://next.material-ui.com/system/basics/#real-world-use-case, it allows removing the Box with the clone prop. It basically allows closing #13100 with a composition demo or Button & Typography. Even complex components can leverage from the layout props (margin, max-width, etc.). Considering the prop was added to the styled() helper, simple or complex, all components can benefit from it, only paying the performance cost when used.
In the case of the Slider, because the color inherits.

I have added the issue we aim to close in the PR's description: #15561.

[oliviertassinari]

Great!

[mnajdova]

I wouldn't recommend adding examples for this per component. Next step will be to introduce a documentation for the sx prop. We will need to re-think the whole system guide, I plan to work on that next week.

[eps1lon]

Could somebody summarize for me what the real-world use case is now? The PR body still has the styling that I wouldn't expect to find anywhere.

[oliviertassinari]

I wonder, did we drop the SliderProps type? Should we do?

diff --git a/packages/material-ui-lab/src/SliderStyled/SliderStyled.d.ts b/packages/material-ui-lab/src/SliderStyled/SliderStyled.d.ts
index 3b80b4c843..3cc143142c 100644
--- a/packages/material-ui-lab/src/SliderStyled/SliderStyled.d.ts
+++ b/packages/material-ui-lab/src/SliderStyled/SliderStyled.d.ts
@@ -36,6 +36,8 @@ export const SliderTrack: React.FC<SliderTrackProps>;
 export const SliderThumb: React.FC<SliderThumbProps>;
 export const SliderValueLabel: React.FC<SliderValueLabel>;

+export type SliderProps = SliderStyledTypeMap['props'];
+
 /**
  *
  * Demos: