[SliderUnstyled] Improved logic for displaying the value label

[ZeeshanTamboli]

• I have followed (at least) the PR section of the contributing guide.

Breaking Changes for MUI Base:

• The valueLabelDisplay prop is removed from SliderUnstyled. The prop was not working as intended in SliderUnstyled (See [docs] Customize valueLabel in SliderUnstyled with tailwind #35398). You can instead provide a valueLabel slot with the slots prop API to show the value label:

-<SliderUnstyled valueLabelDisplay="on" />
+<SliderUnstyled slots={{ valueLabel: SliderValueLabel }} /> 

The following demo shows how to show a value label when it is hovered over with the thumb: https://deploy-preview-35805--material-ui.netlify.app/base/react-slider/#value-label

• The following classes are removed from sliderUnstyledClasses since they are not needed for the value label:

-valueLabel
-valueLabelOpen
-valueLabelCircle
-valueLabelLabel

In the custom value label component, you can define your own classNames and target them with CSS. 

• The SliderValueLabelUnstyled component is removed from SliderUnstyled. You should provide your own custom component for the value label.

• To avoid using React.cloneElement API in value label, the component hierarchy structure of the value label is changed. The value label is now inside the Thumb slot - Thumb -> Input, ValueLabel.

---

Remove the SliderLabelValueUnstyled component from MUI Base and show the value label by simply hovering on the thumb in SliderUnstyled. Add a demo to showcase it (preview below).

Docs Preview: https://deploy-preview-35805--material-ui.netlify.app/base/react-slider/#value-label

Closes #35398

[mnajdova]

I will push a fix for the different prop, it comes from one of the comments from the review on the previous PR.

[ZeeshanTamboli]

@mnajdova It's ready for further review.

[mnajdova]

One last comment, the text in the new demo seems to be a bit off too:

Apart from that it looks good. Great work @ZeeshanTamboli cc @samuelsycamore can you check the copy writing?

[samuelsycamore]

Content looks good, just a couple tiny style things here.

[ZeeshanTamboli]

One last comment, the text in the new demo seems to be a bit off too:

@mnajdova Fixed in commit b439971.

[mnajdova]

Great work @ZeeshanTamboli I don't have anything else to add.