Fix: vendor public libraries are accessible via System.loadLibrary

This CL fixes the problem that vendor public libraries (libs that are
listed in /vendor/etc/public.libraries.txt) are not loadable via
System.loadLibrary(). (Note that the libs were accessible via dlopen()
though.)

The problem was happening because when System.loadLibary() is called,
the classloader first checks whether the lib is found and accessible in
its own native lib search paths. The native lib search paths basically
come from the java.library.path property, which in turn is from
namespace.default.search.path in /system/etc/ld.config.txt. When VNDK is
enforced starting from P, namespace.default.search.path does not have
paths other than /system/lib because otherwise system process can have
unlimited access to libs in vendor partition. The linker namespace is
dynamically configured by the libnativeloader so that only the public
vendor libs are accessible. However, as a side effect of removing
/vendor/lib from namespace.default.search.path, the classloader always
fails to find any lib under /vendor/lib even if the lib is a public one.

In order to solve the problem, while keeping rest of the non-public
vendor libs from apps, /vendor/lib (and /odm/lib and /product/lib as
well) is added to the classloader AFTER native loader is created for the
classloader.

Bug: 93333337
Test: m -j
Test: System.loadLibrary("adsprpc") is successful in Pixel (because
libadsprpc.so is in Pixel's vendor public lib list)
Test: atest cts/tests/tests/jni
Change-Id: Iac12384548cbdd51234568082d02eeba466c160c