Added updateHeight and classes for .v-thumb based on last action

[Refzlund]

The issue

1. When working with absolute divs, the .v-thumb height would not update, when the div would go from absolute to initial positioning.
2. Different transition speeds based on the last scroll action. Ex. you want the the thumb to scroll smoothly, you can do

:global(.v-thumb.wheel) { // When scrolling (using ex. mousewheel)
   transition: .25s ease;
}
:global(.v-thumb.down) { // When dragging the thumb with cursor/touch
   transition: .0s ease;
}
:global(.v-thumb.resize) { // When resizing the thumb
   transition: .5s ease;
}

The approach

Adding a new function for triggering the thumb to update.

/**
   * @type {(divElement: HTMLElement | undefined, minScrollHeight: HTMLElement | undefined) => void} 
   * @param divElement - Will base the new height of this elements scrollheight.
   * This may be wanted if you're working with absolute divs
   * @param minScrollHeight - A reference to an element, which makes up for the minimum scrollheight.
   * (computed: min-height + top,bottom margins + top,bottom border widths)
*/
export async function updateHeight(
    divElement = undefined,
    minScrollHeight = undefined
)

Updated documentation:

working with absolute divs

the Observer WebAPI may not recognize a resize change when working with absolute divs.

you can therefore manually trigger an update calculation, which will update the height of the scrollthumb

/**
  * @type {(divElement: HTMLElement | undefined, minScrollHeight: HTMLElement | undefined) => void} 
  * @param divElement - Will base the new height of this elements scrollheight.
  * This may be wanted if you're working with absolute divs
  * @param minScrollHeight - A reference to an element, which makes up for the minimum scrollheight.
  * (computed: min-height + top,bottom margins + top,bottom border widths)
*/
export async function updateHeight(divElement = undefined, minScrollHeight = undefined)

in this example, we transition from div A to div B.

at the start of the transition, both elements will be absolute, and therefore we trigger an update to the thumb height, so it can transition with the contents.

when the content has finished the transition, the thumb will therefore have smoothly transitioned aswell

the updateHeight in the transitionEnd is just a precaution — but should technically not be necessary

<div class='my-content'>
  <!-- Using the let: directive for updateHeight function -->
  <Svroller(width='100%' height='100%' alwaysVisible!='{true}' let:updateHeight)>
    <MyComponent 
      on:transitionStart={() => updateHeight(elements.divA, elements.view)} 
      on:transitionEnd={updateHeight}
    >
      <div bind:this={elements.view} class='view' style='position: relative; min-height: 400px;'>
        <!-- Transitioning to -->
        <div bind:this={elements.divA} style='position: absolute; left: 500;'>
        <!-- Transitioning from -->
        <div bind:this={elements.divB} style='position: absolute; left: 0;'>
...

<style>
  .my-content :global .v-thumb {
    transition: top .25s ease, height .25s ease;
  }
...