Auto merge of #134625 - compiler-errors:unsafe-binders-ty, r=oli-obk

Begin to implement type system layer of unsafe binders

Mostly TODOs, but there's a lot of match arms that are basically just noops so I wanted to split these out before I put up the MIR lowering/projection part of this logic.

r? oli-obk

Tracking:

- https://github.com/rust-lang/rust/issues/130516

compiler/rustc_lint/src/types.rs

@@ -1284,6 +1284,8 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
                 FfiSafe
             }
 
+            ty::UnsafeBinder(_) => todo!("FIXME(unsafe_binder)"),
+
             ty::Param(..)
             | ty::Alias(ty::Projection | ty::Inherent | ty::Weak, ..)
             | ty::Infer(..)