Rollup merge of #53405 - oconnor663:search_esc, r=GuillaumeGomez

Rollup merge of #53405 - oconnor663:search_esc, r=GuillaumeGomez

restore the page title after escaping out of a search

Currently if I start a search in the docs, but then hit ESC, the "Results for..." title is still there in my browser tab. This is a simple attempt to fix that. I see that there's a separate `var previousTitle = document.title` thing happening in `startSearch()`, but as far as I can tell that's only related to the back stack? I'd also appreciate feedback on the right place to declare the `titleBeforeSearch` variable.

Testing-wise, I've confirmed by hand that the tab title restores correctly after building with `./x.py doc --stage 1 src/libstd`, but nothing more involved than that. What else should I test?