feat(slider): add fullWidth prop (#1354)

The `bx--slider` class in the `Slider` component has max-width of `40rem`. Because `$$restProps` is spread to the top-level `div` element in `Slider`, the only way to override the style is to do so globally:

```css
:global(.bx--slider-container) {
  width: 100%;
}

:global(.bx--slider) {
  max-width: none;
}
```

This adds a `fullWidth` prop that sets a full width style using inline style attributes.

tests/Slider.test.svelte

@@ -10,6 +10,7 @@
   max="{990}"
   maxLabel="990 MB"
   value="{100}"
+  fullWidth
 />
 
 <Slider