Add gen_ndk_usedby_apex.sh script to generate NDK API list used by Mainlain modules when modules get build.
Test: TARGET_BUILD_APPS=com.android.adbd m dist apps_only
Forrest run: android-build.googleplex.com/builds/forrest/run/L97800000742565481
Change-Id: I39e5aa7c74eff46aba06808642b2bd67ae45ba1e