Allow --print=crate-root-lint-levels

[ShE3py]

#13468 delegated all --print requests to rustc; this PR adds an exception to crate-root-lint-levels (rust-lang/rust#139180), i.e.:

$ rustc -Zunstable-options --print=crate-root-lint-levels /dev/null | wc -l
230
$ clippy-driver -Zunstable-options --print=crate-root-lint-levels /dev/null | wc -l
230
$ cargo run --bin clippy-driver -- -Zunstable-options --print=crate-root-lint-levels /dev/null | wc -l
1020

So as to have a way to print all Clippy lint levels in a machine-readable format.

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changelog: none

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[llogiq]

Thank you!