Splits proc_macro::Span::source_text into a new feature gate and stabilizes it.

This rule originated as a `font-size: 16px`, when body had `font-size: 13px`
set in 4fd061c.

It remained even when body's font size was bumped up to 16px,
4d5f4ff, making the rule a no-op, and was
carried forward when it was converted to 1rem in
cc18120.

…text, r=petrochenkov

Stabilize proc_macro::Span::source_text

Splits `proc_macro::Span::source_text` into a new feature gate and stabilizes it. The [FCP is complete](rust-lang#101991 (comment)).

```Rust
impl Span {
    pub fn source_text(&self) -> Option<String>;
}
```

Closes rust-lang#101991

…ing, r=notriddle

Fix item declaration highlighting

Fixes rust-lang#103050.

As mentioned in the issue, rust-lang#102924 introduced this regression. This PR partially reverts it and adds a regression test.

r? `@notriddle`

… r=tmandry

Adjusting test to needs-unwind, with linking issue

Test requires `needs-unwind` (see linked issue rust-lang#103261)

…ize, r=GuillaumeGomez

rustdoc: remove no-op CSS `nav.sub { font-size: 1rem }`

This rule originated as a `font-size: 16px`, when body had `font-size: 13px` set in 4fd061c.

It remained even when body's font size was bumped up to 16px, 4d5f4ff, making the rule a no-op, and was carried forward when it was converted to 1rem in cc18120.

Remove extra spaces in docs

Removing some random extra spaces in the examples for `core::sync::atomic`.

r? `@thomcc`

…ice, r=TaKO8Ki

Erase regions before checking for `Default` in uninitialized binding error

Fixes rust-lang#103250