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

[joserodolfofreitas]

Summary

In a group formed by Row grouping, users want to use Row reordering to apply orders inside a parent's group.

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