lint identity_conversion could be extended to work with try_from/try_into

[tmpolaczyk]

The following code doesn't warn about the useless conversion from u8 to u8:

let a = 0u8;
let b = u8::try_from(a).unwrap();

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The identity_conversion lint currently only supports the traits Into, From, and FromIter. I think it should be simple and useful to extend it to also work with TryFrom and TryInto.

An alternative would be a new lint to warn on usages of try_from when from is enough, but I'm not sure how can that be implemented.