Add grpc_channel_get_info() to C-core API.

include/grpc/grpc.h

include/grpc/impl/codegen/grpc_types.h

src/core/ext/census/grpc_filter.c

src/core/ext/client_channel/client_channel.c

src/core/ext/load_reporting/load_reporting_filter.c

src/core/lib/channel/channel_stack.c

src/core/lib/channel/channel_stack.h

src/core/lib/channel/compress_filter.c

src/core/lib/channel/connected_channel.c

src/core/lib/channel/deadline_filter.c

src/core/lib/channel/http_client_filter.c

src/core/lib/channel/http_server_filter.c

src/core/lib/channel/message_size_filter.c

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

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

src/core/lib/surface/channel.c

src/core/lib/surface/lame_client.c

src/core/lib/surface/server.c

test/core/client_channel/lb_policies_test.c

test/core/end2end/tests/filter_call_init_fails.c