When in remote virtualization scenario, rows need to have recalculated index

[hanastasov]

When using virtualized grid, this.grid.dataRows() will return rows, whose indexes are calculated based on current data view. Current data view contain only the newly fetched rows.

• igniteui-angular version: 13

Steps to reproduce

1. Go to Remote Virtualization Grid dev demo
2. Scroll down the grid so as to see row with ProductID 50 as first row.
3. Read grid.dataRows()[0].index - it is 0. It should be 49 to represent all 49 rows that have gone out of view after scrolling.