Move detection of HTTP CONNECT proxy from DNS resolver to client channel.

BUILD

CMakeLists.txt

Makefile

binding.gyp

build.yaml

config.m4

gRPC-Core.podspec

grpc.gemspec

package.xml

src/core/ext/client_channel/client_channel.c

src/core/ext/client_channel/http_connect_handshaker.c

src/core/ext/client_channel/http_connect_handshaker.h

src/core/ext/client_channel/http_proxy.c

src/core/ext/client_channel/http_proxy.h

src/core/ext/resolver/dns/native/dns_resolver.c

src/python/grpcio/grpc_core_dependencies.py

tools/doxygen/Doxyfile.core.internal

tools/run_tests/generated/sources_and_headers.json

vsprojects/vcxproj/grpc/grpc.vcxproj

vsprojects/vcxproj/grpc/grpc.vcxproj.filters