Pass the base sdk extension version to soong

So that it can be added to the soong config.

Bug: 220086085
Test: m nothing && inspect soong.variables
Change-Id: I949059b9284b16220e2489010279aeae98b4b7fb
diff --git a/core/soong_config.mk b/core/soong_config.mk
index 7f9dbe5..bec63a2 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -28,6 +28,7 @@
 $(call add_json_str,  Platform_sdk_codename,             $(PLATFORM_VERSION_CODENAME))
 $(call add_json_bool, Platform_sdk_final,                $(filter REL,$(PLATFORM_VERSION_CODENAME)))
 $(call add_json_val,  Platform_sdk_extension_version,    $(PLATFORM_SDK_EXTENSION_VERSION))
+$(call add_json_val,  Platform_base_sdk_extension_version, $(PLATFORM_BASE_SDK_EXTENSION_VERSION))
 $(call add_json_csv,  Platform_version_active_codenames, $(PLATFORM_VERSION_ALL_CODENAMES))
 $(call add_json_str,  Platform_security_patch,           $(PLATFORM_SECURITY_PATCH))
 $(call add_json_str,  Platform_preview_sdk_version,      $(PLATFORM_PREVIEW_SDK_VERSION))