Bad tooltip placement for single bars

[nickofthyme]

Describe the bug
When displaying a single bar, stacked or non-stacked, the tooltip is shown within the highlighted area.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://elastic.github.io/elastic-charts/?path=/story/bar-chart--single-data-stacked-chart
2. Hover over the stacked bars
3. Notice the placement of the tooltip

Expected behaviour
The tooltip attempts to place itself outside of the area.

Screenshots

Version (please complete the following information):

• Elastic Charts: 19.8.2

Additional context
Add any other context about the problem here.