Auto merge of #121320 - saethlin:rollup-x1x4toc, r=saethlin

Rollup of 8 pull requests

Successful merges:

 - #120718 (Add "algebraic" fast-math intrinsics, based on fast-math ops that cannot return poison)
 - #121195 (unstable-book: Separate testing and production sanitizers)
 - #121205 (Merge `CompilerError::CompilationFailed` and `CompilerError::ICE`.)
 - #121233 (Move the extra directives for `Mode::CoverageRun` into `iter_header`)
 - #121256 (Allow AST and HIR visitors to return `ControlFlow`)
 - #121307 (Drive-by `DUMMY_SP` -> `Span` and fmt changes)
 - #121310 (Remove an old hack for rustdoc)
 - #121311 (Make `is_nonoverlapping` `#[inline]`)

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

Author: bors

compiler/rustc_ast/src/lib.rs

@@ -12,10 +12,12 @@
 #![allow(internal_features)]
 #![feature(rustdoc_internals)]
 #![feature(associated_type_bounds)]
+#![feature(associated_type_defaults)]
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
 #![cfg_attr(bootstrap, feature(min_specialization))]
+#![feature(never_type)]
 #![feature(negative_impls)]
 #![feature(stmt_expr_attributes)]