Prepare to publish matcher

[natebosch]

Drop -wip from the version and extend the test constraint to allow
the latest.

Add changes to test changelog since it exports the APIs and these
changes are user facing.

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:checks	0.3.2-wip	WIP (no publish necessary)
package:fake_async	1.3.3	already published at pub.dev
package:matcher	0.12.18	ready to publish	matcher-v0.12.18
package:test	1.27.1-wip	WIP (no publish necessary)
package:test_api	0.7.8	already published at pub.dev
package:test_core	0.6.14	ready to publish	test_core-v0.6.14
package:test_descriptor	2.0.2	already published at pub.dev
package:test_process	2.1.1	already published at pub.dev

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[kevmoo]

Can we hold until #2563 lands @natebosch ?

[kevmoo]

Nevermind 😁

Might want to rebase, though...

[github-actions]

PR Health

Changelog Entry ✔️

Package	Changed Files

Changes to files need to be accounted for in their respective changelogs.

This check can be disabled by tagging the PR with skip-changelog-check.