Merge pull request #7640 from markdroth/handshaker_api

...ore/ext/transport/chttp2/client/insecure/channel_create.c

...t/transport/chttp2/client/insecure/channel_create_posix.c

...xt/transport/chttp2/client/secure/secure_channel_create.c

...core/ext/transport/chttp2/server/insecure/server_chttp2.c

...xt/transport/chttp2/server/insecure/server_chttp2_posix.c

...ext/transport/chttp2/server/secure/server_secure_chttp2.c

src/core/ext/transport/chttp2/transport/chttp2_transport.c

src/core/ext/transport/chttp2/transport/chttp2_transport.h

src/core/lib/channel/handshaker.c

src/core/lib/channel/handshaker.h

src/core/lib/http/httpcli_security_connector.c

src/core/lib/security/transport/handshake.c

src/core/lib/security/transport/handshake.h

src/core/lib/security/transport/security_connector.c

src/core/lib/security/transport/security_connector.h

test/core/bad_client/bad_client.c

test/core/end2end/fixtures/h2_sockpair+trace.c

test/core/end2end/fixtures/h2_sockpair.c

test/core/end2end/fixtures/h2_sockpair_1byte.c

test/core/end2end/fuzzers/api_fuzzer.c