Create public stub for platform's sysprop_library

Java modules using SystemAPI can now link against platform owned
sysprop_library with public stub. This allows modules to use platform's
public sysprops (which should be regarded as an API) without any hidden
API usages, if using dynamic linking and boot class path.

This doesn't affect any vendor or odm owned sysprop_library.

Bug: 141246285
Bug: 145167888
Test: m
Change-Id: I99824fb24a75cc8282211c2ad6c6296ae9fca393