Linker namespace changes for moving ICU4C to APEX

libandroidicu is used by various libraries, e.g. libxml2, minikin.
Thus, expose libandroidicu to default namespace.

libpac is only used by libjni_pacprocessor (part of framework).

libicuuc, libicui18n are not exposed to default namespace,
because everyone else, except app, should use libandroidicu.
They are exposed to classloader namespace from runtime namespace
via the work done in libnativeloader in http://r.android.com/887453
b/120786417 has more details about these 2 libraries.

Bug: 120659668
Test: m droid
Change-Id: I2cd3378f1eb94b7bb1c942738b59d7e577a5f8f0