Merge github.com:grpc/grpc into slice_with_exec_ctx

BUILD

CMakeLists.txt

Makefile

build.yaml

doc/connectivity-semantics-and-api.md

gRPC-Core.podspec

grpc.gemspec

include/grpc/impl/codegen/gpr_slice.h

include/grpc/impl/codegen/slice.h

package.xml

src/core/ext/client_channel/client_channel.c

src/core/ext/transport/chttp2/client/chttp2_connector.c

src/core/ext/transport/chttp2/client/chttp2_connector.h

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

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

src/core/ext/transport/chttp2/server/chttp2_server.c

src/core/ext/transport/chttp2/server/chttp2_server.h

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

src/core/lib/channel/handshaker.c

src/core/lib/channel/handshaker.h