Rollup merge of #66704 - GuillaumeGomez:intra-doc-enum-variant-field, r=kinnison

Rollup merge of #66704 - GuillaumeGomez:intra-doc-enum-variant-field, r=kinnison

Intra doc enum variant field

Part of #43466.

Add intra-doc link support for this:

```rust
enum Foo {
    X {
        y: u8, // can be found with Foo::X::y
    }
}
```

r? @kinnison