feat(o11y): reduce visibility of some builder methods in ApiTracerContext

Author: blakeli0

sdk-platform-java/gax-java/gax/src/main/java/com/google/api/gax/tracing/ApiTracerContext.java

@@ -342,7 +342,7 @@ public abstract static class Builder {
 
     public abstract Builder setTransport(@Nullable Transport transport);
 
-    public abstract Builder setOperationType(@Nullable OperationType operationType);
+    abstract Builder setOperationType(@Nullable OperationType operationType);
 
     public abstract Builder setServerPort(@Nullable Integer serverPort);
 
@@ -354,7 +354,7 @@ public abstract static class Builder {
 
     public abstract Builder setUrlDomain(@Nullable String urlDomain);
 
-    public abstract Builder setDestinationResourceIdSupplier(
+    abstract Builder setDestinationResourceIdSupplier(
         @Nullable Supplier<String> destinationResourceIdSupplier);
 
     public abstract ApiTracerContext build();