Copy cargo clean target-dir validation tests to clean_new_layout.rs

[ranger-ross]

What does this PR try to resolve?

#16712 added some additional tests to clean.rs but did not add them to clean_new_layout.rs (which mirrors clean.rs with -Zbuild-dir-new-layout enabled)

While these tests do not depend on the new build-dir layout, #16807 renames clean.rs to clean_legacy_layout.rs and clean_new_layout.rs to clean.rs.
Having the tests be in both makes the switch easier and results in less diffs.

I pulled this out into its own PR as the stabilization has grown pretty large.

How to test and review this PR?

cargo test clean

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• Owners of files modified in this PR: @ehuss, @epage, @weihanglo
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