Add scripts to generate java APIs used by Mainline modules.

Test: TARGET_BUILD_APPS=com.android.adbd m dist apps_only

Change-Id: Icd854fd40c3026ae9aae6dc30c9e79027e1303a0

apex/testing.go

@@ -24,6 +24,7 @@ var PrepareForTestWithApexBuildComponents = android.GroupFixturePreparers(
 	android.MockFS{
 		// Needed by apex.
 		"system/core/rootdir/etc/public.libraries.android.txt": nil,
+		"build/soong/scripts/gen_java_usedby_apex.sh":          nil,
 		"build/soong/scripts/gen_ndk_backedby_apex.sh":         nil,
 		// Needed by prebuilt_apex.
 		"build/soong/scripts/unpack-prebuilt-apex.sh": nil,