`GridModel.clicksToExpand: 1` not respected for full-width group rows

[amcclain]

GridModel supports a clicksToExpand prop, but it is only applied when treeMode == true. We wanted this to work for a simple grouped grid (full width grouping rows).

(More specifically, we wanted it to apply to a grouped DataView, where the client wants all of the groups to be collapsed by default so the user can see a clean list of categories, but then we want it to be trivial to expand any of those groups to see the actual content w/minimal friction).

Curious if there was a reason that we limited this to treeMode only: https://github.com/xh/hoist-react/blob/8d79c7292c1fe469dc6de84dcb24983f30016e2c/cmp/grid/Grid.ts#L849

I also wasn't able to find any native AG Grid option to get this behavior.