fix: tooltip pointer position in hovermode x

[OBe95]

Fixes #6900

If I understood well the logic in hover.js when hovermode === 'x'

• lx represents the center of the highlighted data point
• there is a logic to adapt the tooltip box so that it doesn't go outside of the main-svg
• this logic seems to misplace the center of the tooltip pointer

[archmoj]

Great fix. 🥇
Two minor suggestions and please add draftlogs/6900_fix.md file as described here.
Thank you!

[OBe95]

Thanks for the review @archmoj

[archmoj]

💃