Implement a lint for replacable Command::new

[GnomedDev]

Closes #3436

changelog: [unnecessary_shell_command] Add pedantic lint for shelling out when a Rust solution can be used instead.

[rustbot]

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[matthiaskrgr]

How does the lint reliably determine that an operation is "trivial" ?

When I write a Command that executes sed 's/ *(.*)//; s/>.*//; s/.*[:<] *//' will that also be flagged for being trivial?
or ls -a --inode
or wget -r --level=4 -P somedir someurl1 someurl2 ?

[GnomedDev]

It does not determine of an operation is trivial, that's why it's in pedantic. It simply checks if the string passed to Command::new is one of the strings in a configurable list.

[bors]

☔ The latest upstream changes (presumably #13376) made this pull request unmergeable. Please resolve the merge conflicts.