Fix variable deallocation order in panic unwinding paths

[sladyn98]

This PR fixes a soundness bug where local variables are deallocated out of order during panic unwinding, allowing destructors to access freed memory. This violates Rust's safety guarantees and has caused real-world unsoundness in crates like generatively.

This PR removes the is_generator check and unconditionally emits StorageDead statements during unwinding for ALL functions, bringing non-generator behavior in line with generators. It ensures that during unwinding, when a local variable goes out of scope, its storage is properly marked as dead via StorageDead, allowing the borrow checker to enforce the
invariant that values must outlive their references even in panic paths.

Fixes #147875

[rustbot]

r? @jdonszelmann

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[rustbot]

⚠️ Warning ⚠️

• This PR is based on an upstream commit that is older than 28 days.

  It's recommended to update your branch according to the rustc-dev-guide.

[sladyn98]

r? @dianne

[sladyn98]

CC @traviscross