extras/android: import the libvlc.so build script from libvlcjni

So we can build the Android libvlc.so locally without depending on libvlcjni.

• Tested libvlcjni still builds when using our local script: robUx4/libvlcjni!1
• Tested vlc-android still builds when using the libvlcjni above: vlc-android!1990