As discussed, this streamlines the handling for `basePath` to not automatically strip and add the `basePath` when provided to `next/link` or `router.push/replace` and only automatically adds the `basePath` and when it is manually provided it will cause a 404 which ensures `href` still matches to the pages directory 1-to-1.
This also adds additional test cases that we discussed to ensure this behavior is working as intended
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Fixes#13902
8dd3d2a8e2