upstream: use hash instead of MessageDifferencer for metadata/locality comparison

Replace Protobuf::util::MessageDifferencer with MessageUtil::hash for
equality checks in hot paths to reduce CPU during large EDS updates:

- updateDynamicHostList: metadata comparison (upstream_impl.cc)
- LocalityEndpointEqualTo: locality/endpoint comparison (locality_endpoint.h)

Hash comparison is typically faster than reflection-based MessageDifferencer
and matches Envoy's MessageLiteDifferencer approach when full protos are
disabled. Helps with clusters of ~5k endpoints where these comparisons run
per host on each EDS update.

Signed-off-by: William Dauchy <william.dauchy@datadoghq.com>

Author: wdauchy

source/common/upstream/locality_endpoint.h

@@ -20,8 +20,8 @@ struct LocalityEndpointHash {
 
 struct LocalityEndpointEqualTo {
   bool operator()(const LocalityEndpointTuple& lhs, const LocalityEndpointTuple& rhs) const {
-    return Protobuf::util::MessageDifferencer::Equals(std::get<0>(lhs), std::get<0>(rhs)) &&
-           Protobuf::util::MessageDifferencer::Equals(std::get<1>(lhs), std::get<1>(rhs));
+    return MessageUtil::hash(std::get<0>(lhs)) == MessageUtil::hash(std::get<0>(rhs)) &&
+           MessageUtil::hash(std::get<1>(lhs)) == MessageUtil::hash(std::get<1>(rhs));
   }
 };
 

source/common/upstream/upstream_impl.cc

@@ -2343,11 +2343,11 @@ bool BaseDynamicClusterImpl::updateDynamicHostList(
 
       hosts_changed |= updateEdsHealthFlag(*host, *existing_host->second);
 
-      // Did metadata change?
+      // Did metadata change? Use hash for faster comparison.
       bool metadata_changed = true;
       if (host->metadata() && existing_host->second->metadata()) {
-        metadata_changed = !Protobuf::util::MessageDifferencer::Equivalent(
-            *host->metadata(), *existing_host->second->metadata());
+        metadata_changed =
+            MessageUtil::hash(*host->metadata()) != MessageUtil::hash(*existing_host->second->metadata());
       } else if (!host->metadata() && !existing_host->second->metadata()) {
         metadata_changed = false;
       }