Use newly split feature defaults in plugins and runtimes.

The new fields fixed_features and overridable_features can be simply merged to recover the old aggregate defaults.  By splitting them though, plugins and runtimes get some extra information about lifetimes for enforcement.

PiperOrigin-RevId: 625107741

upb/reflection/file_def.c

@@ -232,20 +232,35 @@ const UPB_DESC(FeatureSet*)
   size_t n;
   const UPB_DESC(FeatureSetDefaults_FeatureSetEditionDefault)* const* d =
       UPB_DESC(FeatureSetDefaults_defaults)(defaults, &n);
-  const UPB_DESC(FeatureSet)* ret = NULL;
+  const UPB_DESC(FeatureSetDefaults_FeatureSetEditionDefault)* result = NULL;
   for (size_t i = 0; i < n; i++) {
     if (UPB_DESC(FeatureSetDefaults_FeatureSetEditionDefault_edition)(d[i]) >
         edition) {
       break;
     }
-    ret = UPB_DESC(FeatureSetDefaults_FeatureSetEditionDefault_features)(d[i]);
+    result = d[i];
   }
-  if (ret == NULL) {
+  if (result == NULL) {
     _upb_DefBuilder_Errf(ctx, "No valid default found for edition %s",
                          upb_FileDef_EditionName(edition));
     return NULL;
   }
-  return ret;
+
+  // Merge the fixed and overridable features to get the edition's default
+  // feature set.
+  const UPB_DESC(FeatureSet)* fixed = UPB_DESC(
+      FeatureSetDefaults_FeatureSetEditionDefault_fixed_features)(result);
+  const UPB_DESC(FeatureSet)* overridable = UPB_DESC(
+      FeatureSetDefaults_FeatureSetEditionDefault_overridable_features)(result);
+  if (!fixed && !overridable) {
+    _upb_DefBuilder_Errf(ctx, "No valid default found for edition %s",
+                         upb_FileDef_EditionName(edition));
+    return NULL;
+  } else if (!fixed) {
+    return overridable;
+  }
+  return _upb_DefBuilder_DoResolveFeatures(ctx, fixed, overridable,
+                                           /*is_implicit=*/true);
 }
 
 // Allocate and initialize one file def, and add it to the context object.