[Help] Distinguish between multiple bar groups when rendering titles

How can I distinguish between multiple `BarChartGroupData` groups in a bar chart when `getTitlesWidget` callback is called. There only seems to be the value which is not enough to determine the group (same value might be in more groups) and meta doesn't seem to contain that info either. How can I determine which group is it?

No file or test is named. Start by tracing the BarChartGroupData model and the getTitlesWidget callback, then inspect the metadata available at that call site. Done requires a clearly specified way to distinguish groups, with the expected callback behavior documented or covered by a test.

Written by the indexing model from the issue text.