This code was calling `sort_unstable_by`, but failed to impose a total order on
the initial spans. That resulted in unpredictable handling of closure spans,
producing inconsistencies in the coverage maps and in user-visible coverage
reports.

This patch fixes the problem by always sorting closure spans before
otherwise-identical non-closure spans, and also switches to a stable sort in
case the ordering is still not total.

Switching to `Ordering::then_with` makes control-flow less complicated, and
there is no need to use `partial_cmp` here.

…, r=compiler-errors

Avoid blessing cargo deps's source code in ui tests

Before this PR, the source code of dependencies was included in UI test error messages whenever possible. Unfortunately, "whenever possible" means in some cases the source code wouldn't be injected, resulting in a test failure.

One such case is when `$CARGO_HOME` is remapped to something that is not present on disk [^1]. As the remapped path doesn't exist on disk, the source code wouldn't be showed in `tests/ui/issues/issue-21763.rs`:

```diff
    = note: required for `hashbrown::raw::RawTable<(Rc<()>, Rc<()>)>` to implement `Send`
 note: required because it appears within the type `HashMap<Rc<()>, Rc<()>, RandomState>`
   --> $HASHBROWN_SRC_LOCATION
-   |
-LL | pub struct HashMap<K, V, S = DefaultHashBuilder, A: Allocator + Clone = Global> {
-   |            ^^^^^^^
 note: required because it appears within the type `HashMap<Rc<()>, Rc<()>>`
   --> $SRC_DIR/std/src/collections/hash/map.rs:LL:COL
 note: required by a bound in `foo`
```

This PR fixes the problem by always hiding dependencies source code in the error messages generated during UI tests. This is implemented with a new internal flag, `-Z ignore-directory-in-diagnostics-source-blocks=$path`, which compiletest passes during UI tests. Once this is merged, remapping the Cargo home will be supported.

This PR is best reviewed commit-by-commit.

[^1]: After being puzzled for a bit, I discovered why this never impacted `rust-lang/rust`: we don't remap `$CARGO_HOME` :sweat_smile:. Instead, we set `$CARGO_HOME` to `/cargo` in CI, which sort-of-but-not-really achieves the same effect.

Make `TyKind::Adt`'s `Debug` impl be more pretty

Currently `{:?}` on `Ty` for a `TyKind::Adt` would print as `Adt(Foo, [])`. This PR changes it to be `Foo` when there are no generics or `Foo<T>`/`Foo<T, U>` when there _are_ generics. Example from debug log:
`├─0ms DEBUG rustc_hir_analysis::astconv return=Bar<T/#0, U/#1>`

I should have done this in my initial PR for a prettier TyKind: Debug impl but I thought I would need to be accessing generics_of to figure out where in the "path" the generics would have to go??? but no, adts literally only have a single place the generics can go (on the end). Feel a bit silly about this :)

r? `@oli-obk`

… r=compiler-errors

Migrate diagnostics in `hir_typeck/src/cast.rs`

coverage: Fix an unstable-sort inconsistency in coverage spans

This code was calling `sort_unstable_by`, but failed to impose a total order on the initial spans. That resulted in unpredictable handling of closure spans, producing inconsistencies in the coverage maps and in user-visible coverage reports.

This PR fixes the problem by always sorting closure spans before otherwise-identical non-closure spans, and also switches to a stable sort in case the ordering is still not total.

---

In addition to the fix itself, this PR also contains a cleanup to the comparison function that I was working on when I discovered the bug.

…notriddle

Move mobile topbar title creation entirely into JS

I was looking at potential size improvements and saw that we had an empty `h2` tag for the mobile topbar title that was filled with JS. So at this point, I think it's fine to just completely generate it from JS, like that the w3c HTML validator will emit one less warning.

r? `@notriddle`

…mulacrum

Add myself to .mailmap

…er-errors

compiletest: Don't swallow some error messages.

This updates some error handling in compiletest to display the underlying error rather than discarding it. There have been cases where the lack of error information makes it difficult to understand what went wrong.

…est, r=notriddle

Update browser-ui-test version

It includes the fix from `@notriddle` (GuillaumeGomez/browser-UI-test#537).

r? `@notriddle`