Merge package:matcher (#2292)

- [x] Move and fix workflow files, labeler.yaml, and badges in the
README.md
- [x] Rev the version of the package, so that pub.dev points to the
correct site
- [x] Add a line to the changelog:
```
* Move to `dart-lang/test` monorepo.
```

- [x] Add the package to the top-level readme of the monorepo:
```
| [matcher](pkgs/matcher/) | Support for specifying test expectations via an extensible Matcher class. Also includes a number of built-in Matcher implementations for common cases. | [![pub package](https://img.shields.io/pub/v/matcher.svg)](https://pub.dev/packages/matcher) |
```

- [ ] **Important!** Merge the PR with 'Create a merge commit' (enabling
then disabling the `Allow merge commits` admin setting)
- [ ] Update the auto-publishing settings on
https://pub.dev/packages/matcher/admin
- [ ] Add the following text to https://github.com/dart-lang/matcher/:'

```
> [!IMPORTANT]  
> This repo has moved to https://github.com/dart-lang/test/tree/master/pkgs/matcher
```

- [ ] Publish using the autopublish workflow
- [ ] Push tags to GitHub using `git tag --list 'matcher*' | xargs git
push origin`
- [ ] Close open PRs in dart-lang/matcher with the following message:

```
Closing as the [dart-lang/matcher](https://github.com/dart-lang/matcher) repository is merged into the [dart-lang/test](https://github.com/dart-lang/test) monorepo. Please re-open this PR there!
```
      
- [ ] Transfer issues by running `dart run
pkgs/repo_manage/bin/report.dart transfer-issues --source-repo
dart-lang/matcher --target-repo dart-lang/test --add-label
package:matcher --apply-changes`
- [ ] Archive https://github.com/dart-lang/matcher/


---

- [x] I’ve reviewed the contributor guide and applied the relevant
portions to this PR.

<details>
  <summary>Contribution guidelines:</summary><br>

- See our [contributor
guide](https://github.com/dart-lang/.github/blob/main/CONTRIBUTING.md)
for general expectations for PRs.
- Larger or significant changes should be discussed in an issue before
creating a PR.
- Contributions to our repos should follow the [Dart style
guide](https://dart.dev/guides/language/effective-dart) and use `dart
format`.
- Most changes should add an entry to the changelog and may need to [rev
the pubspec package
version](https://github.com/dart-lang/sdk/blob/main/docs/External-Package-Maintenance.md#making-a-change).
- Changes to packages require [corresponding
tests](https://github.com/dart-lang/.github/blob/main/CONTRIBUTING.md#Testing).

Note that many Dart repos have a weekly cadence for reviewing PRs -
please allow for some latency before initial review feedback.
</details>

.github/ISSUE_TEMPLATE/matcher.md

@@ -0,0 +1,5 @@
+---
+name: "package:matcher"
+about: "Create a bug or file a feature request against package:matcher."
+labels: "package:matcher"
+---