This change makes it so, instead of mixing string distance with
type unification, function signature search works by
mapping names to IDs at the start, reporting to the user any
cases where it had to make corrections, and then matches with
IDs when going through the items.

This only changes function searches. Name searches are left alone,
and corrections are only done when there's a single item in the
search query.

The number 900 is safely below github's limit of 1000 entries for a directory.
PRs to move tests can still decrease the sizes of various directories,
but adjusting the limit won't be neccessary any more.

In general, the limit is a bad tool to direct people to put tests into
fitting directories because when those are available, usually the limit
is not hit, while the limit is hit in directories that have a weak
substructure themselves.

... with this convertions some tests fail :(

FFX has new builtin support for isolating the daemon's environment. This
switches the manual isolation originally written to that new builtin
feature.

…risDenton

Implement tuple<->array convertions via `From`

This PR adds the following impls that convert between homogeneous tuples and arrays of the corresponding lengths:
```rust
impl<T> From<[T; 1]> for (T,) { ... }
impl<T> From<[T; 2]> for (T, T) { ... }
/* ... */
impl<T> From<[T; 12]> for (T, T, T, T, T, T, T, T, T, T, T, T) { ... }

impl<T> From<(T,)> for [T; 1] { ... }
impl<T> From<(T, T)> for [T; 2] { ... }
/* ... */
impl<T> From<(T, T, T, T, T, T, T, T, T, T, T, T)> for [T; 12] { ... }
```

IMO these are quite uncontroversial but note that they are, just like any other trait impls, insta-stable.

…ou-se

Replace generic thread parker with explicit no-op parker

With rust-lang#98391 merged, all platforms supporting threads now have their own parking implementations. Therefore, the generic implementation can be removed. On the remaining platforms (really just WASM without atomics), parking is not supported, so calls to `thread::park` now return instantly, which is [allowed by their API](https://doc.rust-lang.org/nightly/std/thread/fn.park.html). This is a change in behaviour, as spurious wakeups do not currently occur since all platforms guard against them. It is invalid to depend on this, but I'm still going to tag this as libs-api for confirmation.

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

r? rust-lang/libs

Correctly convert an NT path to a Win32 path in `read_link`

This can be done by simply changing the `\??\` prefix to `\\?\`.

Currently it strips off the prefix which could lead to the wrong path being returned (e.g. if it's not a drive path or if the path contains trailing spaces, etc).

r? libs

…ions, r=GuillaumeGomez

rustdoc: restructure type search engine to pick-and-use IDs

Fixes rust-lang#110029

Preview: https://notriddle.com/rustdoc-demo-html-3/search-corrections/std/index.html?search=-%3E%20streaming

![image](https://user-images.githubusercontent.com/1593513/233494900-ae77d5b4-e395-41f8-bbac-53ee55bb4a76.png)

This change makes it so, instead of mixing string distance with type unification, function signature search works by mapping names to IDs at the start, reporting to the user any cases where it had to make corrections, and then matches with IDs when going through the items.

This only changes function searches. Name searches are left alone, and corrections are only done when there's a single item in the search query.

tests: Add tests for LoongArch64

tidy: remove ENTRY_LIMIT maximum checking and set it to 900

Removes checking of `ENTRY_LIMIT` towards an actually reached maximum, and sets it to 900.

The number 900 is safely below github's limit of 1000 entries for a directory.
PRs to move tests can still decrease the sizes of various directories,
but adjusting the limit won't be neccessary any more. In fact, such reduction PRs are a great idea so that no unrelated PR is hitting the limit: ideally there would always be a (manually maintained) safety margin between the actually reached maximum and `ENTRY_LIMIT`, for all directories.

In general, the limit is a bad tool to direct people to put tests into
fitting directories because when those are available, usually the limit
is not hit, while the limit is hit in directories that have a weak
substructure themselves. I got into this situation myself when writing rust-lang#110694: tests/ui/parser is hitting the limit, but has few directories of its own.

Suggested by `@petrochenkov` in rust-lang#110694 (comment).

r? `@petrochenkov`

Update ICU4X to 1.2

Was released a couple weeks ago.

Also needed to make progress on rust-lang#109302 (though this PR does not achieve that part just yet)

Constify slice flatten method

ACP: rust-lang/libs-team#218

…errors

rustc_middle: Fix `opt_item_ident` for non-local def ids

Noticed while working on rust-lang#110855.

…n, r=tmandry

Use builtin FFX isolation for Fuchsia test runner

FFX has new builtin support for isolating the daemon's environment. This switches the manual isolation originally written to that new builtin feature.

r? ``@tmandry``