Add "jni_libs" property to apex module

Which is the list of JNI libraries that are embeded inside the apex.
jni_libs is handled just like native_shared_libs except that it is
stored in apex_manifest.

When linkerconfig finds an apex with JNI libs, it exposes the namespace
for the apex as visible so that libnativeloader can link the namespace
to the corresponding classloader-namespace.

Bug: 149363889
Test: m nothing(runs soong test)
Change-Id: I52ebe38b44545e6e8853e34a3404a235c858112a