Horizontal row dimension expansion for Pivot Grid

[skrustev]

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

There's a need for a more compact display of row dimension hierarchies, where instead of expanding inner levels of row dimensions vertically, they are rendered horizontally.

Merging of cells also should happen horizontally, when there are collapsed levels for some rows, in order to be visually more clean.

There should be the ability to show additional row displaying the total for the expanded dimension value. It would hide when collapsed, because that would mean two duplicate rows pretty much.

Navigation should be similar to the vertical rendered row dimensions and switching should between the two should be intuitive.

Visually it should looks almost identical, only difference would be the position of the expanded row cells.

Describe the solution you'd like

A new option should be added, that specifies the row layout. A specification can be view here: https://github.com/IgniteUI/igniteui-angular/wiki/igxPivotGrid-Specification#323-row-dimension-expansion

Describe alternatives you've considered

There are no alternatives.

Additional context

Example shown would be something similar to our existing Compact Layout for the XamPivotGrid: https://www.infragistics.com/help/wpf/xampivotgrid-us-compact-layout