Accessibility issues related to stack callouts

[krkshitij]

Following issues have been identified/reported:

1. In AreaChart and LineChart, the stack callout displays data for non-selected legends (lines) when hovered over.

   
   

2. In GroupedVerticalBarChart with stack callout enabled, individual bars within a group can be focused instead of the entire group, and the callout displays data for non-selected legends (bars).

   
   

3. In VerticalStackedBarChart with stack callout enabled and a legend selected, the whole bar can be focused instead of individual bar segments, and the callout displays data for non-selected legends (bar segments).