fix: removes group segment from route id to allow correct resolution of urls

[hawk93]

closes #14062

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[eltigerchino]

Thanks for the PR! A changeset is needed for patch fixes like this one.

[PatrickG]

I'm not sure if this should be merged, see my comment in the issue.

[Rich-Harris]

Agree with @PatrickG — you can either pass a RouteId or a Pathname. I think it's better to enforce this throughout, rather than allowing either of those or a secret third option, because you will end up with inconsistencies in your app otherwise.

For completeness: if we were to do this the logic would need tweaking — it only adds de-grouped route IDs for dynamic routes, and doesn't e.g. add /blah for /(group)/blah.