Warn and fix missing mime types

[Archmonger]

Issues

N/A

Summary

Windows registry can sometimes go corrupt causing missing mime types. This results in our backends assuming all file types are text/plain. Ultimately, this causes us to fail to serve our ReactPy client index.js.

This PR aims to only resolve a minimal set of file extensions (only the ones we potentially use within ReactPy core). I considered using a more comprehensive mime_types list from this repo, but it seems a bit overkill for us right now. We may want to use it if we need to serve a variety of static files.

Checklist

• Tests have been included for all bug fixes or added functionality.
• The changelog.rst has been updated with any significant changes.

[rmorshea]

I'll review this evening.

[rmorshea]

I wonder if we should be really trying to patch this or just warning about it and linking to resources on the Windows mimetype registry - neither Starlette nor Flask appear to make any similar attempt.

[Archmonger]

I thought the same thing at first.

But the patch is a harmless fix for reactpy.run, which is a user's first impression of our framework. If we can improve first impressions with minimal LOCs it's in our best interest to do so.

I didn't want to link to anything specific since the repair method depends on operating system. This issue technically isn't limited to Windows, but it is far more likely to happen on Windows.

I will update the comment to be more specific about this issue being OS independent.

[rmorshea]

I just merged a fix for the test-docs failure.

[rmorshea]

After that last comment LGTM