This PR fixes an issue where the context menu in the keymap UI would be
immediately dismissed after being opened when using a trackpad on MacOS.

Right clicking on MacOS almost always fires a scroll event with a delta
of 0 pixels right after (which is not the case when using a mouse). The
fired scroll event caused the context menu to be removed on the next
frame. This change ensures the menu is only removed when a vertical
scroll is actually happening.

Release Notes:

- N/A