Related to
#433

Textual formats often have either encoding or column errors.

This is a common issue, see e.g.
https://duckdb.org/docs/data/csv/reading_faulty_csv_files.html

We just ignore them.

This commit modifies the backend code to convert the input CSV into an
`NgramsList`, so that we can reuse the JSON API for the upload.

it also brings the CSV and JSON APIs closer in look.
Temporarily disable the `importCsvFile` function.

This commit fixes a bug (or feature? unclear at this stage) of the
`rootOf` function inside `searchTableNgrams`, which could, in some
occasion, return a root which has a different `ListType`, which
in turn throws off pagination.