Only handle "Select All" when Term has focus

[JJJ]

Fixes #6733.

[JJJ]

I purposely am opting to use vanilla JS here (instead of internal Hyper/React properties) with future-proofing in mind.

I originally started trying to stop this from inside of the SearchBox component, but the only approach I could think of was more invasive (importing Hyper/Term) while also only targeting keydown on the SearchBox input.

Doing this from inside the Hyper container ensures that if some other input (say, that a plugin might introduce) has focus, the "Select All" attempt will not be handled then either.

---

Another search-specific code change could be:

    if (term && !term.props.search) {
      term.selectAll();
    }