Better handling of cancellation, uri parse errors, and disconnection

src/core/channel/client_channel.c

src/core/client_config/resolver_registry.c

src/core/client_config/subchannel.c

src/core/client_config/uri_parser.c

src/core/client_config/uri_parser.h

src/core/surface/server.c

src/core/transport/chttp2_transport.c

test/core/client_config/uri_parser_test.c