Answer a refused field value with 400, not 500

[ramonski]

Description of the issue/feature this PR addresses

A value the schema will not take comes from the request, so it is a bad request. The field managers raise a bare TypeError or ValueError for these, which plone.jsonapi.core renders as a 500: the caller is told the server broke when in fact the payload did.

It also costs the error its identity. A caller writing many objects in one run can catch an APIError and carry on, naming the object that failed, but a TypeError carries nothing to distinguish a refused value from a genuine fault inside the server, so it has to be let through and ends the whole run with the field name and nothing else.

Current behavior before PR

POST /senaite/@@API/senaite/v1/update/<uid>
{"sort_key": 1}

HTTP/1.1 500 Internal Server Error
{"message": "sort_key: wrong type", ...}

Desired behavior after PR is merged

HTTP/1.1 400 Bad Request
{"message": "sort_key: wrong type", ...}

Four raise sites, all of them reporting a value that arrived in the payload: a wrong type, a field that failed its own validator, and two copies of "multiple values for a single valued field". The messages are unchanged, only the exception type is, from TypeError/ValueError to BadRequestError.

Verification

• POST a wrong-typed value (an int into a schema.Float) and a value that fails a field validator; both answer 400 with the same message as before.
• A value the schema accepts is unaffected.