[Slider] Center value label for disabled slider

[davidfdriscoll]

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

This PR correctly centers a value label for a disabled slider, resolving this issue, by removing a fix for IE 11. It also removes the same fix from the customized slider demos and adds a simple test for a disabled slider with an active value label.

Closes #19329

<Slider
  color="success"
  value={value}
  step={10}
  marks
  valueLabelDisplay="auto"
  onChange={handleChange}
  aria-labelledby="continuous-slider"
/>

[mui-pr-bot]

Details of bundle changes (experimental)

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