Check responsiveness of http/3 server when running.
Also, a test case with http/2 or http/3 server requirement
now implicitly drags in a 'http' server and we need no longer
mention that in testdata.
Closes#15058
Some feature names used in tests had minor differences compared to
the well-known ones from `curl -V`. This patch syncs them to make test
results easier to grok.
Closes#14183
