rustdoc search engine: tab key should iterate over "Types/modules", "As parameters" and "As return value"

[dns2utf8]

Maybe shift+tab should jump reverse.

The arrow keys up and down are currently used to walk through the results and left right are for navigating the query. To me this feels natural so I would keep it.

cc @GuillaumeGomez

[GuillaumeGomez]

I like this idea so I implement it!

[dns2utf8]

Cool, I think #45288 fixes that

[GuillaumeGomez]

It does. :)