Bug brushing Heatmap with small multiples

[nickofthyme]

Describe the issue

When using the Heatmap with SmallMultiples, the brush incorrectly determines the selected cell range.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://codesandbox.io/s/brave-maria-19rofp?file=/src/App.tsx
2. Brush on the first panel in the first column of cells
3. Notice the correct brushing range is highlighted
4. Brush the last column in the first panel
5. Notice the highlighter brush selection is on the second panel

Expected behaviour

Correct range is highlighted

Screenshots

Version (please complete the following information):

• Elastic Charts: main

Additional context
There was an issue with this when developing that selected the actual column plus 1 due to the use of bisectLeft function. But that was supposedly fixed and may be related or not.

Kibana Cross Issues
Needed for elastic/kibana#154434

Checklist

• The proper chart type label has been added (e.g. :xy, :partition)
• The proper feature labels have been added (e.g. :interactions, :axis)
• Every related Kibana issue is listed under Kibana Cross Issues list and the kibana cross issue tag is applied