Support diagonal mouse movement in new flyout menus

What does this MR do and why?

Implements Add tolerance for diagonal mouse movement from ... (#419813 - closed) by adding two dynamically positioned SVG polygons as extra hover targets.

Screenshots or screen recordings

recording_1691762957

How to set up and validate locally

1. Enable super_sidebar_flyout_menus feature flag: echo "Feature.enable(:super_sidebar_flyout_menus)" | rails c

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.