fix(sparklines): tooltip behaviour in safari

This commit fixes an issue that happens when a group of tooltips are rendered in safari: when hovering over the group of charts quickly sometimes tooltips are not hidden.

The root cause for the issue was the usage of debounceByAnimationFrame for the mouse event that triggered the tooltips. It would create a race condition with the mouseLeave event of the component.

The solution moves handling of showing the tooltip to the chart instance by leveraging the formatter callback option, instead of using a DOM event.

before	after
sparkline_tooltips_safari	sparkline_tooltips_safari_after

Closes #517 (closed)