extend redundant_allocation to Arc

[lengyijun]

Currently redundant_allocation check Rc and Box. And it can be extended to Arc, which is quite similar to Rc.
redundant_allocation should check:

Arc<Arc<T>>
Arc<Box<T>>
Arc<&T>

If it's ok, I can give a pr.

[xFrednet]

Thanks for taking over the implementation of this issue. You can comment @rustbot claim to assign the issue to yourself. That also indicates to others that someone is working on it, and you can unassign yourself at any time. 🙃

@rustbot label +C-enhancement +good-first-issue

[lengyijun]

@rustbot claim