9e73d33680
Clippy pointer cast lint experiment This PR is an experiment about exposing more parts of `rustc_typeck` for use in `clippy`. In particular, the code that checks where a cast is valid or not was exposed, which necessitated exposing [`FnCtxt`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_typeck/check/struct.FnCtxt.html), and figuring out how to create an instance of that type inside `clippy`. This was prompted by [this clippy issue](https://github.com/rust-lang/rust-clippy/issues/2064). r? @oli-obk