Before the documentation sometimes referred to an "rwlock" and sometimes to "`RwLock`".

…gling references

When this was added, the sidebar had a bit more complex style. It can be
removed, now.

Remove unused variable in float formatting.

Consistently write `RwLock`

Before the documentation sometimes referred to an "rwlock" and sometimes to "`RwLock`".

Never panic in `thread::park` and `thread::park_timeout`

fixes rust-lang#102398

`@rustbot` label +T-libs +T-libs-api

…r=m-ou-se

scoped threads: pass closure through MaybeUninit to avoid invalid dangling references

The `main` function defined here looks roughly like this, if it were written as a more explicit stand-alone function:
```rust
// Not showing all the `'lifetime` tracking, the point is that
// this closure might live shorter than `thread`.
fn thread(control: ..., closure: impl FnOnce() + 'lifetime) {
    closure();
    control.signal_done();
    // A lot of time can pass here.
}
```
Note that `thread` continues to run even after `signal_done`! Now consider what happens if the `closure` captures a reference of lifetime `'lifetime`:
- The type of `closure` is a struct (the implicit unnameable closure type) with a `&'lifetime mut T` field. References passed to a function are marked with `dereferenceable`, which is LLVM speak for *this reference will remain live for the entire duration of this function*.
- The closure runs, `signal_done` runs. Then -- potentially -- this thread gets scheduled away and the main thread runs, seeing the signal and returning to the user. Now `'lifetime` ends and the memory the reference points to might be deallocated.
- Now we have UB! The reference that as passed to `thread` with the promise of remaining live for the entire duration of the function, actually got deallocated while the function still runs. Oops.

Long-term I think we should be able to use `ManuallyDrop` to fix this without `unsafe`, or maybe a new `MaybeDangling` type. I am working on an RFC for that. But in the mean time it'd be nice to fix this so that Miri with `-Zmiri-retag-fields` (which is needed for "full enforcement" of all the LLVM flags we generate) stops erroring on scoped threads.

Fixes rust-lang#101983
r? `@m-ou-se`

…, r=m-ou-se

fix backtrace small typo

Move lifetime resolution module to rustc_hir_analysis.

Now that lifetime resolution has been removed from it, this file has nothing to do in `rustc_resolve`.  It's purpose is to compute Debruijn indices for lifetimes, so let's put it in type collection.

… r=GuillaumeGomez

rustdoc: remove unneeded `<div>` wrapper from sidebar DOM

When this was added, the sidebar had a bit more complex style. It can be removed, now.

Preview: https://notriddle.com/notriddle-rustdoc-demos/sidebar-block/std/index.html