[data grid] Tree data: Change a row's displayed order inside its parent group.

[joserodolfofreitas]

Summary

In a tree hierarchy, users may want to use Row reordering to change the order inside a parent.

The internal order of the rows in a given group is updated, with the possibility to make the order persistent through the callback onRowOrderChange. In this case, oldIndex and targetIndex is based only on the indexes inside the given group.

Extracted from: #4821