[xDS] move CDS and EDS watchers into xds resolver (grpc#35011)

Closes grpc#35011

COPYBARA_INTEGRATE_REVIEW=grpc#35011 from markdroth:xds_watchers_in_xds_resolver c3ab5b9
FUTURE_COPYBARA_INTEGRATE_REVIEW=grpc#35011 from markdroth:xds_watchers_in_xds_resolver c3ab5b9
PiperOrigin-RevId: 583525309

Author: markdroth

BUILD

@@ -583,7 +583,6 @@ GRPC_XDS_TARGETS = [
     "//src/core:grpc_lb_policy_cds",
     "//src/core:grpc_lb_policy_xds_cluster_impl",
     "//src/core:grpc_lb_policy_xds_cluster_manager",
-    "//src/core:grpc_lb_policy_xds_cluster_resolver",
     "//src/core:grpc_lb_policy_xds_override_host",
     "//src/core:grpc_lb_policy_xds_wrr_locality",
     "//src/core:grpc_lb_policy_ring_hash",