Rustdoc-Json: List `impl`s for primitives

[aDotInTheVoid]

#![feature(no_core)]
#![feature(rustdoc_internals)]
#![no_core]

pub trait Local {}

impl Local for bool {}

#[doc(primitive = "bool")]
/// Boolean docs
mod prim_bool {}

Gives

"0:3:366": {
      "attrs": ["#[doc(primitive = \"bool\")]"],
      "crate_id": 0,
      "deprecation": null,
      "docs": "Boolean docs",
      "id": "0:3:366",
      "inner": "bool",
      "kind": "primitive_type",
      "links": {},
      "name": "bool",
      "span": {
        "begin": [12, 0],
        "end": [12, 16],
        "filename": "/data/ne321/rust/src/test/rustdoc-json/impls/local_for_local_primitive.rs"
      },
      "visibility": "public"
    }

but doesn't show the trait impls for bool.

@rustbot modify labels: +A-rustdoc-json +T-rustdoc