Add environment variable UNBUNDLED_BUILD_TARGET_SDK_WITH_DESSERT_SHA

UNBUNDLED_BUILD_TARGET_SDK_WITH_DESSERT_SHA enables user to specify
${codename}.${sha} as min_sdk_version and target_sdk_version in order to
support mainline train building into android build.

Test: TH
Bug: 295905124
Change-Id: I6c793bc83e88ec620ed5e2e87d0371bc2455cf1b
diff --git a/core/android_manifest.mk b/core/android_manifest.mk
index ff49262..7f46903 100644
--- a/core/android_manifest.mk
+++ b/core/android_manifest.mk
@@ -51,6 +51,9 @@
         my_target_sdk_version := $(my_target_sdk_version).$$(cat $(API_FINGERPRINT))
         my_min_sdk_version := $(my_min_sdk_version).$$(cat $(API_FINGERPRINT))
         $(fixed_android_manifest): $(API_FINGERPRINT)
+      else ifdef UNBUNDLED_BUILD_TARGET_SDK_WITH_DESSERT_SHA
+        my_target_sdk_version := $(UNBUNDLED_BUILD_TARGET_SDK_WITH_DESSERT_SHA)
+        my_min_sdk_version := $(UNBUNDLED_BUILD_TARGET_SDK_WITH_DESSERT_SHA)
       endif
     endif
   endif