Reorganize ext tree

- filters live under filters
- lb_policy, resolver implementations (being part of client_channel) live under client_channel
diff --git a/config.m4 b/config.m4
index 6e6a65a..86f1564 100644
--- a/config.m4
+++ b/config.m4
@@ -259,47 +259,47 @@
     src/core/tsi/transport_security.c \
     src/core/ext/transport/chttp2/server/chttp2_server.c \
     src/core/ext/transport/chttp2/client/secure/secure_channel_create.c \
-    src/core/ext/client_channel/channel_connectivity.c \
-    src/core/ext/client_channel/client_channel.c \
-    src/core/ext/client_channel/client_channel_factory.c \
-    src/core/ext/client_channel/client_channel_plugin.c \
-    src/core/ext/client_channel/connector.c \
-    src/core/ext/client_channel/http_connect_handshaker.c \
-    src/core/ext/client_channel/http_proxy.c \
-    src/core/ext/client_channel/lb_policy.c \
-    src/core/ext/client_channel/lb_policy_factory.c \
-    src/core/ext/client_channel/lb_policy_registry.c \
-    src/core/ext/client_channel/parse_address.c \
-    src/core/ext/client_channel/proxy_mapper.c \
-    src/core/ext/client_channel/proxy_mapper_registry.c \
-    src/core/ext/client_channel/resolver.c \
-    src/core/ext/client_channel/resolver_factory.c \
-    src/core/ext/client_channel/resolver_registry.c \
-    src/core/ext/client_channel/retry_throttle.c \
-    src/core/ext/client_channel/subchannel.c \
-    src/core/ext/client_channel/subchannel_index.c \
-    src/core/ext/client_channel/uri_parser.c \
+    src/core/ext/filters/client_channel/channel_connectivity.c \
+    src/core/ext/filters/client_channel/client_channel.c \
+    src/core/ext/filters/client_channel/client_channel_factory.c \
+    src/core/ext/filters/client_channel/client_channel_plugin.c \
+    src/core/ext/filters/client_channel/connector.c \
+    src/core/ext/filters/client_channel/http_connect_handshaker.c \
+    src/core/ext/filters/client_channel/http_proxy.c \
+    src/core/ext/filters/client_channel/lb_policy.c \
+    src/core/ext/filters/client_channel/lb_policy_factory.c \
+    src/core/ext/filters/client_channel/lb_policy_registry.c \
+    src/core/ext/filters/client_channel/parse_address.c \
+    src/core/ext/filters/client_channel/proxy_mapper.c \
+    src/core/ext/filters/client_channel/proxy_mapper_registry.c \
+    src/core/ext/filters/client_channel/resolver.c \
+    src/core/ext/filters/client_channel/resolver_factory.c \
+    src/core/ext/filters/client_channel/resolver_registry.c \
+    src/core/ext/filters/client_channel/retry_throttle.c \
+    src/core/ext/filters/client_channel/subchannel.c \
+    src/core/ext/filters/client_channel/subchannel_index.c \
+    src/core/ext/filters/client_channel/uri_parser.c \
     src/core/ext/transport/chttp2/client/chttp2_connector.c \
     src/core/ext/transport/chttp2/server/insecure/server_chttp2.c \
     src/core/ext/transport/chttp2/server/insecure/server_chttp2_posix.c \
     src/core/ext/transport/chttp2/client/insecure/channel_create.c \
     src/core/ext/transport/chttp2/client/insecure/channel_create_posix.c \
-    src/core/ext/lb_policy/grpclb/grpclb.c \
-    src/core/ext/lb_policy/grpclb/grpclb_channel_secure.c \
-    src/core/ext/lb_policy/grpclb/load_balancer_api.c \
-    src/core/ext/lb_policy/grpclb/proto/grpc/lb/v1/load_balancer.pb.c \
+    src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.c \
+    src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_channel_secure.c \
+    src/core/ext/filters/client_channel/lb_policy/grpclb/load_balancer_api.c \
+    src/core/ext/filters/client_channel/lb_policy/grpclb/proto/grpc/lb/v1/load_balancer.pb.c \
     third_party/nanopb/pb_common.c \
     third_party/nanopb/pb_decode.c \
     third_party/nanopb/pb_encode.c \
-    src/core/ext/lb_policy/pick_first/pick_first.c \
-    src/core/ext/lb_policy/round_robin/round_robin.c \
-    src/core/ext/resolver/dns/c_ares/dns_resolver_ares.c \
-    src/core/ext/resolver/dns/c_ares/grpc_ares_ev_driver_posix.c \
-    src/core/ext/resolver/dns/c_ares/grpc_ares_wrapper.c \
-    src/core/ext/resolver/dns/native/dns_resolver.c \
-    src/core/ext/resolver/sockaddr/sockaddr_resolver.c \
-    src/core/ext/load_reporting/load_reporting.c \
-    src/core/ext/load_reporting/load_reporting_filter.c \
+    src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.c \
+    src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.c \
+    src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.c \
+    src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_ev_driver_posix.c \
+    src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.c \
+    src/core/ext/filters/client_channel/resolver/dns/native/dns_resolver.c \
+    src/core/ext/filters/client_channel/resolver/sockaddr/sockaddr_resolver.c \
+    src/core/ext/filters/load_reporting/load_reporting.c \
+    src/core/ext/filters/load_reporting/load_reporting_filter.c \
     src/core/ext/census/base_resources.c \
     src/core/ext/census/context.c \
     src/core/ext/census/gen/census.pb.c \
@@ -629,15 +629,15 @@
   PHP_ADD_BUILD_DIR($ext_builddir/src/boringssl)
   PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/census)
   PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/census/gen)
-  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/client_channel)
-  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/lb_policy/grpclb)
-  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/lb_policy/grpclb/proto/grpc/lb/v1)
-  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/lb_policy/pick_first)
-  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/lb_policy/round_robin)
-  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/load_reporting)
-  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/resolver/dns/c_ares)
-  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/resolver/dns/native)
-  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/resolver/sockaddr)
+  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/filters/client_channel)
+  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/filters/client_channel/lb_policy/grpclb)
+  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/filters/client_channel/lb_policy/grpclb/proto/grpc/lb/v1)
+  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/filters/client_channel/lb_policy/pick_first)
+  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/filters/client_channel/lb_policy/round_robin)
+  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/filters/client_channel/resolver/dns/c_ares)
+  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/filters/client_channel/resolver/dns/native)
+  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/filters/client_channel/resolver/sockaddr)
+  PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/filters/load_reporting)
   PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/transport/chttp2/alpn)
   PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/transport/chttp2/client)
   PHP_ADD_BUILD_DIR($ext_builddir/src/core/ext/transport/chttp2/client/insecure)