Add fake resolver for tests.

Makefile

build.yaml

src/core/ext/resolver/sockaddr/sockaddr_resolver.c

test/core/client_config/lb_policies_test.c

test/core/end2end/fake_resolver.c

test/core/end2end/fake_resolver.h

test/cpp/grpclb/grpclb_test.cc

tools/run_tests/sources_and_headers.json

vsprojects/vcxproj/grpc_test_util/grpc_test_util.vcxproj

...cts/vcxproj/grpc_test_util/grpc_test_util.vcxproj.filters

...j/grpc_test_util_unsecure/grpc_test_util_unsecure.vcxproj

...est_util_unsecure/grpc_test_util_unsecure.vcxproj.filters