Addanewlint`ptr_as_ptr`

This PR adds a new lint

which checks for

casts between raw pointers without changing its mutability and suggest replacing it with

. Closes #5890.

Open question: should this lint be

or

? I set it

for now because the original post suggests using it, but I think the lint also fits well to

.

changelog: New lint

该提问来源于开源项目：rust-lang/rust-clippy