Error-document status reflects a uniform error set, and a typed exception supplies its own

AbstractErrorDocument::getStatusCode() rounded every multi-error document to the nearest status class, so a bag of validation errors that all share status 422 collapsed to 400 — wrong for the common case where an adapter reports several field violations at once. It now returns the shared status verbatim when every error carries the same one, and only falls back to the rounding heuristic for a genuinely mixed set. Separately, ErrorResponse::fromException() now threads the exception's declared getStatusCode() as the document's explicit status, so a typed JsonApiExceptionInterface (e.g. an adapter's 422 validation-failed exception) renders with the status it declares rather than one re-derived from its error objects. Both were surfaced building the haddowg/json-api-symfony Validator bridge, whose multi-violation 422s otherwise mis-statused as 400.