igx-tree-grid: excel-style filtering should show children of parent elements returned from the filter

[kdinev]

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

Currently, when using the igx-tree-grid excel style filtering, I only see specific elements matching the applied filter, but all their children are excluded from the filter, unless they also match the current filter. This makes the filtering behavior not very suitable for scenarios where filtering is applied to parent-level elements, in order to view their children. E.g. org chart - we filter by manager to see their reports; investment portfolios - we filter by portfolio to view the corresponding investment items; inventory management - we filter by location to see available inventory only for the specific location. There's many other examples.

Describe the solution you'd like

I would like ESF to present me with filtered-in items` children either by default, or via setting.

Describe alternatives you've considered

The excel style filtering can order values in a tree, instead of just a flat list. This way I can take advantage of cascade selection and have all children selected by default. I can even exclude certain items if I have a very specific scenario, which requires that.

Additional context

Add any other context or screenshots about the feature request here.