Reorder `walk_` functions in intravisit.rs
Reorder the `walk_` functions to match the order of the `visit_` methods. This is a follow up to https://github.com/rust-lang/rust/pull/103692.
Note that there are some oddballs. I put them where I thought made the most sense:
```diff
$ diff \
<(sed -n 's/^.*\<fn visit_\([^(]*\).*$/\1/;T;p' compiler/rustc_hir/src/intravisit.rs) \
<(sed -n 's/^.*\<fn walk_\([^<]*\).*$/\1/;T;p' compiler/rustc_hir/src/intravisit.rs)
1,5d0
< nested_item
< nested_trait_item
< nested_impl_item
< nested_foreign_item
< nested_body
9,10d3
< id
< name
20c13
< array_length
---
> array_len
30a24
> fn_ret_ty
31a26
> fn_kind
41c36
< variant_data
---
> struct_def
46c41
< infer
---
> inf
54d48
< attribute
```
Also, as some weak evidence that i did things correctly, I get the following before and after the change:
```sh
$ sort compiler/rustc_hir/src/intravisit.rs | openssl sha256
SHA256(stdin)= cac13d2545731ef442f318e2b4286490d7ac5494f4ad10c4cf4c5d4f50d21641
```
r? `@fee1-dead`
5a288dc112