tests: update some HTTP/2 over HTTPS tests

- improve descriptions
- require http/2, not h2c, since they are done over HTTPS

Closes #15317

tests: check http/2 and http/3 server responsiveness

Check responsiveness of http/3 server when running.

Also, a test case with http/2 or http/3 server requirement
now implicitl

tests: check http/2 and http/3 server responsiveness

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

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tests: sync feature names with `curl -V`

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
res

tests: sync feature names with `curl -V`

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

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test2406: verify -f with HTTP/2