Add LOCAL_SDK_VERSION := system_$(VER)

The system_$(VER) can be set in LOCAL_SDK_VERSION, and the apk will use
android_system.jar at build time.
If LOCAL_SDK_VERSION is not defined and this module is installed in
vendor.img, LOCAL_SDK_VERSION is set to system_current.

Bug: 67724799
Test: 1. build && run on taimen
2. LOCAL_SDK_VERSION:=system_27 in ims.apk && build ims.apk && check
the vsdk_v27_intermediates.

Change-Id: I5b11c78b8fcd4a2f2a5e3b141527cd34dbe80018
diff --git a/core/java.mk b/core/java.mk
index 45d5678..99dc9fc 100644
--- a/core/java.mk
+++ b/core/java.mk
@@ -135,7 +135,7 @@
   ifneq (,$(LOCAL_SDK_VERSION))
     # Set target-api for LOCAL_SDK_VERSIONs other than current.
     ifneq (,$(filter-out current system_current test_current, $(LOCAL_SDK_VERSION)))
-      renderscript_target_api := $(LOCAL_SDK_VERSION)
+      renderscript_target_api := $(call get-numeric-sdk-version,$(LOCAL_SDK_VERSION))
     endif
   endif  # LOCAL_SDK_VERSION is set
 endif  # LOCAL_RENDERSCRIPT_TARGET_API is set
@@ -820,8 +820,8 @@
 endif  # full_classes_jar is defined
 
 ifneq (,$(filter-out current system_current test_current, $(LOCAL_SDK_VERSION)))
-  my_default_app_target_sdk := $(LOCAL_SDK_VERSION)
-  my_sdk_version := $(LOCAL_SDK_VERSION)
+  my_default_app_target_sdk := $(call get-numeric-sdk-version,$(LOCAL_SDK_VERSION))
+  my_sdk_version := $(call get-numeric-sdk-version,$(LOCAL_SDK_VERSION))
 else
   my_default_app_target_sdk := $(DEFAULT_APP_TARGET_SDK)
   my_sdk_version := $(PLATFORM_SDK_VERSION)