[igx-grid] expose grid.verticalScrollContainer.igxForOf as dataView property

[tkiryu]

Is your feature request related to a problem? Please describe.

Before, I asked you to expose filteredSotedData property as a public API. Because I wanted to get dataView.

#1432

filteredSotedData made my demand at that time . But it is not enough now becauseigx-grid has grouping feature and then filteredSotedData is not equal to the dataView when grouping.

Instead, grid.verticalScrollContainer.igxForOf is exactly the dataView what I want.

Describe the solution you'd like

I'd like you to expose grid.verticalScrollContainer.igxForOf as dataView property like this.

// grid-base.component.ts
get dataView(): any[] {
  return this.grid.verticalScrollContainer.igxForOf;
}

// how to use
const dataView = this.grid.dataView;

Describe alternatives you've considered

I have no choice but to use this.grid.verticalScrollContainer.igxForOf directly. But it is not a public API(I thought it was not marked as hidden before...).

https://github.com/IgniteUI/igniteui-angular/blob/7.3.4/projects/igniteui-angular/src/lib/grids/grid-base.component.ts#L1715-L1719

Additional context

None.