Having a function `to_usize` that does not return a usize is somewhat confusing

Transition future compat lints to {ERROR, DENY} - Take 2

Follow up to rust-lang#63247 implementing rust-lang#63247 (comment).

- `legacy_ctor_visibility` (ERROR) -- closes rust-lang#39207
- `legacy_directory_ownership` (ERROR) -- closes rust-lang#37872
- `safe_extern_static` (ERROR) -- closes rust-lang#36247
- `parenthesized_params_in_types_and_modules` (ERROR) -- closes rust-lang#42238
- `duplicate_macro_exports` (ERROR)
- `nested_impl_trait` (ERROR) -- closes rust-lang#59014
- `ill_formed_attribute_input` (DENY) -- transitions rust-lang#57571
- `patterns_in_fns_without_body` (DENY) -- transitions rust-lang#35203

r? @varkor
cc @petrochenkov

Remove "here" from "expected one of X here"

rename Memory::get methods to get_raw to indicate their unchecked nature

Some recent Miri PRs started using these methods when they should not; this should discourage their use.

In fact we could make these methods private to the `interp` module as far as Miri is concerned -- with the exception of the `uninit` intrinsic which will hopefully go away soon. @bjorn3 @oli-obk does priroda need these methods? It would be great to be able to seal them away.

miri: Rename to_{u,i}size to to_machine_{u,i}size

Having a function `to_usize` that does not return a (host) usize is somewhat confusing, so let's rename it.

r? @oli-obk

`MethodSig` -> `FnSig` & Use it in `ItemKind::Fn`

In both AST & HIR, rename `MethodSig` to `FnSig` and then proceed to use it in `ItemKind::Fn` so that the overall structure is more regular.

r? @davidtwco