Reset highlighted result to top result when backspacing through search

[niquewoodhouse]

Your use case

Problem

As noted in some web feedback captured as part of #19706 when typing for something, people might type a word, get to 0 results and then use backspace to try a different search. They then struggle to use their keyboard to go to their preferred result. This is because:

• When they got 0 results: the browse public rooms became highlighted
• When they backspaced and entered an amended search term, public rooms was still highlighted ¹.

Task

• Experiment with making backspace reset the highlight to be the first result

Notes

¹ This might be part of the reason for #20184

[t3chguy]

This would break the expectations as defined by WAI-ARIA and worsen accessibility I believe. I will dig up the relevant gospel on Monday