feat: type resolve with the correct trailing slash option

[jycouet]

If we have routes/path-a/+page.svelte

The function resolve() propose us two options today

resolve('/path-a')
resolve('/path-a/')

As trailing slash default is never, I would expect that resolve('/path-a/') is not available.
If you set always, I would expect only resolve('/path-a/') to be available.

This PR is addressing this.
But... not that happy that:

• I have to read in packages/kit/src/core/sync/create_manifest_data/index.js
• didn't manage to use https://github.com/jycouet/kit/blob/7acee7aef9ac80614f9a78635cdf4a2a23785961/packages/kit/src/exports/vite/static_analysis/index.js#L213 as it's async

I added a few unit tests to help playing around.
Any help on the stuff I'm not happy about ?

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Preview: https://svelte-dev-git-preview-kit-15027-svelte.vercel.app/