Handle dev-dependency cycles
cc https://github.com/rust-lang/rust-analyzer/issues/14167
This should fix cycles errors mostly (it fixes the one on rome/tools at least, but not on rustc. Though there it might just be because of rustc workspace being rustc workspace). Unfortunately this will effectively duplicate all crates currently, since if we want to be completely correct we'd need to set the test cfg for all dev dependencies and the transitive dependencies of those, something I worry we should try to avoid.
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