Add a hook to Package.Builder.Helper that gets called by PackageFunction after the Package is fully loaded.

--
MOS_MIGRATED_REVID=124260910
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/BlazeRuntime.java b/src/main/java/com/google/devtools/build/lib/runtime/BlazeRuntime.java
index 3a51bb7..4e9de80 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/BlazeRuntime.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/BlazeRuntime.java
@@ -1262,7 +1262,8 @@
 
       Package.Builder.Helper packageBuilderHelper = null;
       for (BlazeModule module : blazeModules) {
-        Package.Builder.Helper candidateHelper = module.getPackageBuilderHelper();
+        Package.Builder.Helper candidateHelper =
+            module.getPackageBuilderHelper(ruleClassProvider, directories.getFileSystem());
         if (candidateHelper != null) {
           Preconditions.checkState(packageBuilderHelper == null,
               "more than one module defines a package builder helper");