test(node,node-core): Add span streaming integration tests (#19806)

Extends our Node (core) integration test runner API to expect `span`
envelopes with both an API to test against span envelope headers as well
as the container. In addition, this adds a couple of integration tests
testing manually started spans, span name updates and span
relationships. Luckily, all of the span relationship logic is
independent from span streaming so the tests all pass. I still believe
it's valuable to have a `span` version of them.