Popperjs is excessively creating new instances for external tooltips

[nickofthyme]

Describe the issue
When using a tooltip synced across multiple charts, the performance can quickly be diminished. The main culprit in that the createPopper method is called on every mouse move, due to the settings changes on each render.

To Reproduce
Steps to reproduce the behavior:

1. Go to this story
2. Place a log within this hook via chrome source lookup.
3. Notice the log is called to update the popperSettings on every mouse change for each external chart.

Expected behaviour
popperSettings are not excessively updated unnecessarily.

Version (please complete the following information):

• Elastic Charts: latest