…facts-flag, r=ecstatic-morse

Populate liveness facts when calling `get_body_with_borrowck_facts` without `-Z polonius`

For a new feature of [Flowistry](https://github.com/willcrichton/flowistry), a static-analysis tool, we need to obtain a `mir::Body`'s liveness facts using `get_body_with_borrowck_facts` (added in rust-lang#86977). We'd like to do this without passing `-Z polonius` as a compiler arg to avoid borrow checking the entire crate.

Support for doing this was added in rust-lang#88983, but the Polonius input facts used for liveness analysis are empty. This happens because the liveness input facts are populated in `liveness::generate` depending only on the value of `AllFacts::enabled` (which is toggled via compiler args).

This PR propagates the [`use_polonius`](https://github.com/rust-lang/rust/blob/8b09ba6a5d5c644fe0f1c27c7f9c80b334241707/compiler/rustc_borrowck/src/nll.rs#L168) flag to `liveness::generate` to support populating liveness facts without requiring the `-Z polonius` flag.

This fix is somewhat patchy - if it'd be better to add more widely-accessible state (like `AllFacts::enabled`) I'd be open to ideas!

…th-coverage, r=ecstatic-morse

Fix switch on discriminant detection in a presence of coverage counters

Fixes rust-lang#93848.

r? ``@ecstatic-morse``

Add one more case to avoid ICE

Fix for the  rust-lang#94291, added one more case to related function to avoid ICE.

Not sure if my test is in the correct place 😅

… r=scottmcm

Remove needless borrows from core::fmt

`check_used` should only look at actual `used` attributes

cc? rust-lang#94348
r? ``@nikic``