Add support for tree data in aggrid

[bigfatwhale]

Add support for tree-styled data in aggrid. See here for aggrid documentation of the feature.

I think we just need to update the logic here -> https://github.com/justpy-org/justpy/blob/master/justpy/templates/js/vue/aggrid.js#L18. The following code should work,

if (key==='getDataPath')) { eval('def[key] = ' + def[key]); }

[bigfatwhale]

Hi @WolfgangFahl, this issue should be fixed judging from the example in https://github.com/justpy-org/justpy/blob/f63e99935769751ab33e1553b852c68b798956c6/examples/grids_tutorial/field_evaluation/grid_test9.py?

Shall we close it?