Introduce TARGET_BUILD_UNBUNDLED_IMAGE

- TARGET_BUILD_UNBUNDLED_IMAGE is similar to TARGET_BUILD_APPS, but
its targets are the unbundled partitions instead of apps.
- Rename TARGET_BUILD_APPS_USE_PREBUILT_SDK to TARGET_BUILD_USE_PREBUILT_SDKS
because it is used even without TARGET_BUILD_APPS.
-Instead of TARGET_BUILD_APPS, use TARGET_BUILD_USE_PREBUILT_SDKS
to build java modules with prebuilt sdks, and propagate to Soong.

Bug: 160390776
Test: TARGET_BUILD_UNBUNDLED_IMAGE=true m vendorimage
Change-Id: Ie096212ccbcca0018baae55e106af693b002c9e5
diff --git a/core/android_manifest.mk b/core/android_manifest.mk
index 8fab9c6..254e09b 100644
--- a/core/android_manifest.mk
+++ b/core/android_manifest.mk
@@ -45,7 +45,7 @@
 my_min_sdk_version := $(call module-min-sdk-version)
 
 ifdef TARGET_BUILD_APPS
-  ifndef TARGET_BUILD_APPS_USE_PREBUILT_SDK
+  ifndef TARGET_BUILD_USE_PREBUILT_SDKS
     ifeq ($(my_target_sdk_version),$(PLATFORM_VERSION_CODENAME))
       ifdef UNBUNDLED_BUILD_TARGET_SDK_WITH_API_FINGERPRINT
         my_target_sdk_version := $(my_target_sdk_version).$$(cat $(API_FINGERPRINT))