Move resolv_init out and make callbacks of libnetd_resolv global

1. Revise init flow of libnetd_resolv
   - A better and generic design for it
2. Rename and make callbacks from netd global
   - libnetd_resolv has multiple components need to use it
   - res* component could use it easily

Bug: 126141549
Test: built, flashed, booted
      system/netd/tests/runtests.sh pass

Change-Id: Iacb4fd708a26fd9c9139a606f0320fc12b4fc7e1