[Material v5] Support mkdocs-localsearch plugin

I checked that…

• … the documentation does not mention anything about my idea
• … to my best knowledge, my idea wouldn’t break something for other users
• … there are no open or closed issues that are related to my idea

Description

As discussed in #1306 and mkdocs/mkdocs#1805, Material v5 breaks support for mkdocs-localsearch.

To support the plugin and enable local search (file:// protocol), changes are required on your side.

AFAIK, there are two major issues preventing local search using Material and current browsers:

1. The search index is stored as a JSON, but loading JSONs isn’t allowed on file protocol due to CORS.
   For Material v4, the mkdocs-localsearch plugin fixes this issue using a modified fetch() call. For Material v5, the same can be achieved, e.g., by modifying ajax() as outlined here, but there’s probably a better solution.
2. The new v5 search engine uses a web worker, but in Chrome, web workers aren’t allowed on file protocol.
   Since this is a new issue, this hasn’t been addressed by mkdocs-localsearch before. A possible solution has been outlined here and here.

I don’t expect Material to support local search natively, but it would be great to be able to add that functionality using a plugin and without having to fork the entire Material project.

Any help is much appreciated.

Use Cases

An MkDocs site is stored and accessed by users locally (file:// protocol), e.g., because the files are distributed with a desktop software. Users want to perform search on that site.

[wilhelmer]

[wilhelmer]

Yes. I hereby solemnly declare that through the tireless work of @squidfunk, mkdocs-localsearch has risen from the dead and we have a working version for v5! 🎉