ReactPy ASGI Middleware and standalone ReactPy ASGI App

[Archmonger]

Issues

• fix ReactPy ASGI App and Middleware #1110

Solution

Create a ReactPy ASGI application that can also function as middleware.

Features of the ASGI application/middleware

• Gain compatibility with every ASGI framework.
• Allows ReactPy to be "self contained" if needed (run within any ASGI webserver without a backend).
• Allows ReactPy to auto-serve web modules.

Things to deprecate:

• reactpy.backend.*.configure is no longer needed.

Checklist

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

[Archmonger]

The more I develop this, the more I realize it's unwise to finish this PR until the following issues are closed

• Modify SimpleReactPyClient to not use pre-defined endpoints #1079
• Embedding ReactPy via Template Tags #653

This PR is in a 90% finished state, but I will hold off on finishing it for now and refocus on template tags.

[Archmonger]

@rmorshea I will implement things using starlette for static files now, but ideally I don't want a web framework to be a dependency for us.

I would feel more comfortable using whitenoise as it's a static-file focused library that doesn't have extra stuff. However, this relies on this PR getting merged:

• FORKED: AsgiWhiteNoise and async WhiteNoiseMiddleware evansd/whitenoise#359

[Archmonger]

Note to self:
It seems logical to mandate that ReactPy standalone's root component must be a html.html node. By forcing the user to template the whole page, this would eliminate the need for a janky Options(head=...) parameter.

html.html(
    {"lang": "en"},
    html.head(
        ...,
    ),
    html.body(
        ...,
    ),
)

It also seems logical to have ReactPyStandalone and ReactPyMiddleware to be discrete classes.

[Archmonger]

The whitenoise maintainers have largely been MIA, so I went ahead and forked it into my own package ServeStatic.

This PR is no longer blocked.