VaScrollbar component rework

[aluarius]

Live examples:

• https://quasar.dev/vue-components/scroll-area
• https://element-plus.org/en-US/component/scrollbar.html#max-height

References:

• https://www.jqwidgets.com/vue-components-documentation/documentation/jqxscrollbar/vue-scrollbar-getting-started.htm
• https://binaryify.github.io/vue-custom-scrollbar/en/#how-to-use

Props:

• alwaysVisible: boolean - flag, indicating if scrollbar should be always visible.
• delay: number - disappear (after container size change, after scroll) delay in ms.
• dark: boolean - notifies scrollbar, that content has dark background.
• tag: string - element tag (div as default).
• speed: number - scroll speed for scrollTo, setScrollTop & setScrollLeft methods.

Emits:

• on:scroll: object - payload contains information about current scroll state (vertical/horizontal position in px, vertical/horizontal scroll progress in px, vertical/horizontal scroll progress in %, height/width of the container in px).

Mehods:

• getScroll - the same as on:scroll object.
• scrollTo - scroll by { x, y } coordinates.
• setScrollTop - set y scroll value (mb it's redundant).
• setScrollLeft - set x scroll value (mb it's redundant).

Usage example:

<va-scrollbar always-visible class="classes overriding-classes">
  Long content.
</va-scrollbar>

Notes

• See also #2400

[xx13]

add to my to-do list ✅

[asvae]

We might want to investigate scrollbar customization possibility in context of this task.