fix: resolve_route prevent dropping a trailing slash of id

[yuki0418]

Issue #14047

Previous PR was #14065, but it was actually just support a trailing slash for type Pathname, not solving the issue.
Apologize about that I misunderstood the issue.

Problem was resolve() from @app/paths drops trailing slash (technically resolve_route() in resolve() does).
For example resolve('/hoge/huga/') returns string of /hoge/huga

Change to keep the trailing slash if id has the trailing slash.

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Preview: https://svelte-dev-git-preview-kit-14294-svelte.vercel.app/

[yuki0418]

Should I handle the trailing slash in resolve() function instead of inside of this function?