Linting public reexport of private dependencies

[mladedav]

Part of public/private dependencies #44663
Partially addresses #71043

I'm adding a warning for reexports of private dependencies into rustc_resolve. I get that this should not be a warning, but should instead be a lint to be controlled by the feature gate, but I did not figure out how exactly to do that at that point. I tried doing the same thing as is done in rustc_privacy, but the linting system is not ready yet as far as I understand the error I got, so I made a warning for now instead. Some guidance on how to emit lints with dcx would be appreciated.

This also sets the std_detect crate as a public dependency of std because some macros are reexported from there. I did not check closer, but the other option may be to allow the specific reexports instead.

[rustbot]

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[compiler-errors]

r? petrochenkov perhaps

[bors]

☔ The latest upstream changes (presumably #143888) made this pull request unmergeable. Please resolve the merge conflicts.