Introduce BOARD_CURRENT_API_LEVEL_FOR_VENDOR_MODULES

If BOARD_CURRENT_API_LEVEL_FOR_VENDOR_MODULES has a numeric value,
it replaces "current" or "system_current" with the version which
the flag indicates.

Bug: 163009188
Test: BOARD_CURRENT_API_LEVEL_FOR_VENDOR_MODULES=29 m, and then check if every vendor
java module's sdk_version is 29 if its sdk_version was current.

Change-Id: I8c7cf21563b984b8e9ef398192031b1f66d96494
diff --git a/core/base_rules.mk b/core/base_rules.mk
index ddf736b..a0b1761 100644
--- a/core/base_rules.mk
+++ b/core/base_rules.mk
@@ -115,6 +115,7 @@
 
 include $(BUILD_SYSTEM)/local_vndk.mk
 include $(BUILD_SYSTEM)/local_systemsdk.mk
+include $(BUILD_SYSTEM)/local_current_sdk.mk
 
 my_module_tags := $(LOCAL_MODULE_TAGS)
 ifeq ($(my_host_cross),true)