Extend //test/integration tests that run against H1 and H2 so they also run against H3/QUIC

HTTP integration test cases like those defined in //test/integration:protocol_integration_test should be run against HTTP3/QUIC when the QUIC extension is enabled in order to ensure that H1, H2 and H3 have the same functionality and semantics. Some of the functionality tested by H2 only tests may also apply to H3/QUIC since the two protocols have similar semantics; also consider extending those tests so they run against QUIC when the extension is enabled.