Create rust-interop.md

[stephane-archer]

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Fixes dart-lang/sdk#59610

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[MaryaBelanger]

Thanks for the work @stephane-archer, these packages are really great!

However, we don’t typically promote third party packages on their own pages on dart.dev due to uncertainty about maintenance and upkeep over time.

I'm going to close these, and instead include your packages and their descriptions in an interop overview page. That'll be less overhead for us but also probably better exposure for your work! Thanks again!

[stephane-archer]

@MaryaBelanger that's a great solution, the goal was for people to be aware of these bindings because they are not in the official documentation while they are possible. Any hint of their existence in documentation makes me happy :)