add sources.toml with the top 400 sources of crates.io, gathered by a modified version of cargo-prefetch

[matthiaskrgr]

still needs some local testing

[flip1995]

In its current state, this repo can't handle config files, other that "passes.toml" and "integration.toml" (because everything is hardcoded 😄). But this gives incentive to improve the tool and make it less hard coded.

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I think this list can be useful to test for ICEs before a release. I'm unsure if it helps with triaging new lints, because the log file will be enormously big and convoluted. But I think we should include it.

[flip1995]

I invited you to the repo. So feel free to change things and push directly to the master main (it will take years until I get used to this...) branch. This is in a prototype state until we want to move it to rust-lang.