Rollup merge of #142208 - Urgau:dead_code-const_, r=petrochenkov

Always consider `const _` items as live for dead code analysis

This PR alters dead code analysis to always consider `const _: () = { ... };` to be live.

This doesn't address the `_name` pattern from rust-lang/rust#142075.

Fixes rust-lang/rust#142104

Author: tgross35