Rollup merge of #117679 - aDotInTheVoid:yes-core, r=GuillaumeGomez

tests/rustdoc-json: Avoid needless use of `no_core` and `lang_items`

See #117487 for motivation.

I've split it into three commits, depending on how much work it was to remove `#![no_core]`. The first is entirely mechanical, the second makes no logical changes but couldn't be done with find+replace, and the third required rewriting assertions no not depend on having `#![no_core]`. All of the interesting changes for review are in the third commit, so I recommend reviewing commit-by-commit.

After this, 3 tests still use `#![no_core]`:

- `./tests/rustdoc-json/primitives/primitive_impls.rs`. Uses impls on primitives, so needs to simulate core
- `./tests/rustdoc-json/primitives/local_primitive.rs`: Uses `rustc_doc_primitive`, so needs to simulate core
- `./tests/rustdoc-json/impls/auto.rs`: Uses auto traits, so needs to simulate core

But after this change, we only rely on the core-rustc boundary in tests that deliberately test those interactions.

r? ``@GuillaumeGomez``

Fixes #117487

Author: GuillaumeGomez

tests/rustdoc-json/doc_hidden_failure.rs

@@ -1,8 +1,5 @@
 // Regression test for <https://github.com/rust-lang/rust/issues/98007>.
 
-#![feature(no_core)]
-#![no_core]
-
 mod auto {
     mod action_row {
         pub struct ActionRowBuilder;

tests/rustdoc-json/enums/field_hidden.rs

@@ -1,11 +1,5 @@
 // Regression test for <https://github.com/rust-lang/rust/issues/100529>.
 
-#![no_core]
-#![feature(no_core, lang_items)]
-
-#[lang = "sized"]
-trait Sized {}
-
 // @has "$.index[*][?(@.name=='ParseError')]"
 // @has "$.index[*][?(@.name=='UnexpectedEndTag')]"
 // @is "$.index[*][?(@.name=='UnexpectedEndTag')].inner.variant.kind.tuple" [null]