Add missing hiddenapi product variables to Soong config

If72bd1c20b2014d0a3d400624d37fdb0a3052245 failed to propagate
PRODUCT_HIDDENAPI_STUBS* to Soong.

Bug: 124316921
Test: m out/soong/hiddenapi/hiddenapi-flags.csv, check previously
      blacklisted classes are now whitelisted.

Change-Id: I9b4a364654bad77b38ceb7062dafaeeab5f49517
diff --git a/core/soong_config.mk b/core/soong_config.mk
index 1f2e258..1fb0c29 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -158,6 +158,10 @@
 $(call add_json_bool, EnforceSystemCertificate,          $(ENFORCE_SYSTEM_CERTIFICATE))
 $(call add_json_list, EnforceSystemCertificateWhitelist, $(ENFORCE_SYSTEM_CERTIFICATE_WHITELIST))
 
+$(call add_json_list, ProductHiddenAPIStubs,             $(PRODUCT_HIDDENAPI_STUBS))
+$(call add_json_list, ProductHiddenAPIStubsSystem,       $(PRODUCT_HIDDENAPI_STUBS_SYSTEM))
+$(call add_json_list, ProductHiddenAPIStubsTest,         $(PRODUCT_HIDDENAPI_STUBS_TEST))
+
 $(call add_json_map, VendorVars)
 $(foreach namespace,$(SOONG_CONFIG_NAMESPACES),\
   $(call add_json_map, $(namespace))\