Remove space after negative sign in Literal to_string

Negative proc macro literal tokens used to be printed with a space between the minus sign and the magnitude. That's because `impl ToString for Literal` used to convert the Literal into a TokenStream, which splits the minus sign into a separate Punct token.

```rust
Literal::isize_unsuffixed(-10).to_string()  // "- 10"
```

This PR updates the ToString impl to directly use `rustc_ast::token::Lit`'s ToString, which matches the way Rust negative numbers are idiomatically written without a space.

```rust
Literal::isize_unsuffixed(-10).to_string()  // "-10"
```

Rollup of 8 pull requests

Successful merges:

 - rust-lang#81797 (Add `core::stream::from_iter`)
 - rust-lang#87267 (Remove space after negative sign in Literal to_string)
 - rust-lang#87663 (Rustdoc accessibility: use an icon for the [-]/[+] controls)
 - rust-lang#87720 (don't use .into() to convert types to identical types (clippy::useless_conversion))
 - rust-lang#87723 (Use .contains instead of manual reimplementation.)
 - rust-lang#87729 (Remove the aarch64 `crypto` target_feature)
 - rust-lang#87731 (Update cargo)
 - rust-lang#87734 (Test dropping union fields more)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup