Rollup merge of #75459 - RalfJung:local-info, r=oli-obk
Rollup merge of #75459 - RalfJung:local-info, r=oli-obk

fix LocalInfo doc comment

The doc comment makes it sound like this is diagnostics-only, but that is not true -- even [unsafety checking uses this information](https://github.com/rust-lang/rust/blob/ded20c98be8585b2a9fe4eeadd1be5524f6ffb17/src/librustc_mir/transform/check_unsafety.rs#L206), so it is crucial for soundness, not just "nice to have".

Cc @oli-obk

graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust