[Do not review] C ffi updates plan

[MaryaBelanger]

trafficstars

This PR is an outline of how to incorporate the content @craiglabenz wrote here (access required) into the C-interop page.

The outline is still very rough, but I suspect the goal is to completely reorganize the site page to present package:ffigen as the default option, show how to use it, and then end the page with the lower level reference info for non-ffigen C-interop stuff that's exists there now.

[dart-github-bot]

Visit the preview URL for this PR (updated for commit 09214372eddfd6d11f61939a889622f9ef531b97):

https://dart-dev--pr5269-c-ffi-hqjps1e6.web.app

[sfshaza2]

@MaryaBelanger, feel free to close this PR, unless you would rather not. You can always open a clean one.

[MaryaBelanger]

Closing for a fresh PR