Introduce the product variable PRODUCT_EXPORT_RUNTIME_APIS

PRODUCT_EXPORT_RUNTIME_APIS is a product variable that inherits the
behavior of the build flag RELEASE_EXPORT_RUNTIME_APIS, which is being
removed. This will be utilized in the product `sdk_with_runtime_apis`,
which will be introduced in a future change.

Test: m nothing --no-skip-soong-tests
Bug: 326312949
Change-Id: I4966b7bfc7423db049acfcede67233352ba8341b
diff --git a/core/product.mk b/core/product.mk
index f0071db..60cab47 100644
--- a/core/product.mk
+++ b/core/product.mk
@@ -458,6 +458,8 @@
 
 _product_single_value_vars += PRODUCT_HIDDEN_API_EXPORTABLE_STUBS
 
+_product_single_value_vars += PRODUCT_EXPORT_RUNTIME_APIS
+
 .KATI_READONLY := _product_single_value_vars _product_list_vars
 _product_var_list :=$= $(_product_single_value_vars) $(_product_list_vars)
 
diff --git a/core/soong_config.mk b/core/soong_config.mk
index e77defb..b43a952 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -402,6 +402,8 @@
 
 $(call add_json_bool, HiddenapiExportableStubs, $(filter true,$(PRODUCT_HIDDEN_API_EXPORTABLE_STUBS)))
 
+$(call add_json_bool, ExportRuntimeApis, $(filter true,$(PRODUCT_EXPORT_RUNTIME_APIS)))
+
 $(call json_end)
 
 $(file >$(SOONG_VARIABLES).tmp,$(json_contents))