Rollup merge of #72968 - integer32llc:docs-arrow-keys, r=GuillaumeGomez
Rollup merge of #72968 - integer32llc:docs-arrow-keys, r=GuillaumeGomez

Only highlight doc search results via mouseover if mouse has moved

## What happens

- Go to https://doc.rust-lang.org/stable/std/index.html
- Put your mouse cursor somewhere in the middle where search results will appear and then don't move the mouse
- Press 's' to focus the search box
- Type a query that brings up enough search results to go under where your mouse cursor is
- Press the down arrow
- The search result that is one below where your mouse cursor is will be highlighted.

## What I expected

When not currently using the mouse, I expect doing a search and then pressing the down arrow to always highlight the first search result immediately below the search box.

## The fix

This feels a bit hacky to me; I'm open to other solutions. This introduces a global JS var that keeps track of whether the person searching has moved their mouse after doing a search or not, and only uses the mouse position to highlight search results if the person HAS moved the mouse AFTER doing a search.

graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust