Fix conformance to SPARQL Update / Query's prefix declaration

Snippet of an example request:

PATCH https://example.org/test.ttl  HTTP/1.1
Content-Type: application/sparql-update

PREFIX acl: <http://www.w3.org/ns/auth/acl#>

Snippet of an example response:

HTTP/1.1 400 Bad Request
X-Powered-By: solid-server/5.7.11
Accept-Patch: application/sparql-update
Content-Type: text/plain; charset=utf-8
Content-Length: 206

Patch document syntax error: Line 1 of <https://example.org/test.ttl>: Bad syntax:
   Unknown syntax at start of statememt: 'PREFIX acl: <http://'/
   at: "PREFIX acl: <http://www.w3.org/"

AFAICT, https://github.com/linkeddata/rdflib.js/issues/651 captures the issue in that NSS rejects SPARQL Update requests with valid payload using PREFIX (and accepts invalid payload containing @prefix).

Nenhum arquivo do repositório ou teste é especificado. Comece reproduzindo a solicitação PATCH com Content-Type application/sparql-update e a declaração PREFIX e, em seguida, compare o comportamento do parser com rdflib.js issue 651; considera-se concluído quando payloads PREFIX válidos são aceitos, enquanto o tratamento de @prefix inválido segue a conformidade SPARQL pretendida.