[Draft] Adds popUntil to GoRouter and its extension

[chunhtai]

fixes flutter/flutter#131625

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[ValentinVignal]

@chunhtai I sent you a message on Discord to suggest another signature for popUntil because I'm trying to make the RouteMatchList a tree. Maybe it would be nice to talk about it?

[chunhtai]

@chunhtai I sent you a message on Discord to suggest another signature for popUntil because I'm trying to make the RouteMatchList a tree. Maybe it would be nice to talk about it?

Which channel did you send the message? I didn't see any notification. Can you ping me on the hackers-routing- channel?

Yes, we should definitely talk about it if this doesn't work well with the new RouteMatchList.

[flodaniel]

@chunhtai is there a result to the discussion around this and relation to a new RouteMatchList? I was just looking for this feature.

[chunhtai]

Close for now until i have time to come back to this pr