[WC-3146] Improve virtual scrolling in data grid 2

[r0b1n]

Pull request type

Bug fix / New feature

---

Description

With recent improvements of virtual scrolling we introduced an issue with horizontal scroll where vertical scrollbar goes out of sight. To mitigate this we took a new approach and improved vertical scrolling even more. This gives the users ability scroll in both directions and have more natural look and feel when virtual scrolling is enabled.

As a small feature we introduced shadows when the grid is scrolled, so the users immediately see that the grid is in the middle of the scroll, this is a good QoL improvement.

What should be covered while testing?

• Check that with fixed scrollbars (usually Windows) and with hide-able scrollbars (usually Mac) alignment of the header and columns work as expected.
• Check that non-virtual scrolling still works as before.