Add note explaining OnlyBodies filter better

compiler/rustc_middle/src/hir/nested_filter.rs

@@ -3,6 +3,10 @@ use rustc_hir::intravisit::nested_filter::NestedFilter;
 /// Do not visit nested item-like things, but visit nested things
 /// that are inside of an item-like.
 ///
+/// Notably, possible occurrences of bodies in non-item-like things
+/// include: closures/generators, inline `const {}` blocks, and
+/// constant arguments of types, e.g. in `let _: [(); /* HERE */];`.
+///
 /// **This is the most common choice.** A very common pattern is
 /// to use `visit_all_item_likes()` as an outer loop,
 /// and to have the visitor that visits the contents of each item