Viewport issue on slider

https://github.com/jlmakes/scrollreveal/assets/69580797/591fd11f-e3ab-4030-9b88-664ce7766582

Replacing the following lines in `isElementVisible()` function solves the problem of viewport issue on slider.
```
function isElementVisible(element) {
...
var elementRect = element.node.getBoundingClientRect();
var geoBounds = element.geometry.bounds;
var highestBound = {
left: Math.min(elementRect.left, geoBounds.left),
right: Math.max(elementRect.right, geoBounds.right),
top: Math.max(elementRect.top, geoBounds.top),
bottom: Math.max(elementRect.bottom, geoBounds.bottom),
}

var elementBounds = {
top: highestBound.top + element.geometry.height * viewFactor,
right: highestBound.right - element.geometry.width * viewFactor,
bottom: highestBound.bottom - element.geometry.height * viewFactor,
left: highestBound.left + element.geometry.width * viewFactor
};
....
}
```

https://github.com/jlmakes/scrollreveal/assets/69580797/32b2e091-6f58-4598-83f0-434b9aa8fd52

But, you have to call ScrollReveal().delegate() function on the corresponding event listeners. Because ScrollReveal.js only works on scroll and resize event.

Start with the isElementVisible() function and reproduce the viewport issue on the slider shown in the linked examples. Check how the element rectangle and geometry bounds determine visibility, and inspect the related ScrollReveal().delegate() event listeners. Done means slider elements receive the expected reveal behavior when their viewport position changes, not only on scroll or resize.

Written by the indexing model from the issue text.