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feat(virtual-scroll): port web components virtual scroll improvements (#17660)

* feat(virtual-scroll): port web components virtual scroll improvements

Apply the igniteui-webcomponents virtual scroll changes since 7.4.0
that fit the Angular version.

- Recycle item elements. `@for ... track $index` rebinds every element
  on each scroll step; the new internal `igxVsRecycle` directive keeps
  the elements of staying items, hands leaving ones to entering items,
  and keeps the focused element in place.
- Add `keyFunction`, so an element follows its item when `data`
  reorders.
- Size unmeasured items by the average measured size, so the scrollbar
  tracks the real content.
- Fix `nearest` alignment for items larger than the viewport; it now
  follows the CSSOM scroll-into-view rules.
- Rewrite the CHANGELOG entry as one new-component entry; the component
  is unreleased.

* fix: tabs component spec RTL tests spilling into virtual scroll test bed

* fix(virtual-scroll): address SSR and sizing issues

- Hydration claims server-rendered views in creation order, but the
  first render created them back to front, reversing the list.
- Angular's server DOM has no getRootNode, so a server re-render threw.
- Past the browser scroll limit, the total sets the DOM-to-virtual
  ratio, so a new average estimate moved rendered items. Later
  averages no longer apply while the list is, or would become,
  compressed.
- An orientation switch kept the previous axis's sizes and average.

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Co-authored-by: Stamen Stoychev <sstoychev@infragistics.com>

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