Feat: Support search without requiring a web server

[Gerrit0]

Search Terms

search.js, search index not available

Problem

See #1247 (comment)

Is there a strong reason for the removal of this search.js? Being able to open the files directly in my browser is a quick way to make sure the pages load as expected. I don't know how much work it is to maintain it, but it seems like it introduces friction to have to spin up a server just to load what would otherwise be static HTML files. - @Fleker

Suggested Solution

Partially revert #1252, creating search.js instead of search.json, and loading that in the theme with a <script defer tag. document.write shouldn't be required.