Add cargo dev setup toolchain

[Alexendoo]

Adds a cargo dev setup toolchain subcommand that creates a rustup toolchain with symlinks to the local cargo-clippy and clippy-driver. Allows you to then do cargo +clippy clippy in other projects to run the locally built Clippy

Sometimes more convenient when you're testing changes on a separate project than cding back & forth to use cargo dev lint [project]

changelog: none

[rustbot]

r? @llogiq

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[llogiq]

There's a lot to unwrap() here, pun intended. I guess for an internal tool that's ok though.

Thank you for building this.

@bors r+

[bors]

📌 Commit 1fff3be has been approved by llogiq

It is now in the queue for this repository.

[bors]

⌛ Testing commit 1fff3be with merge 1ba7821...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: llogiq
Pushing 1ba7821 to master...