Move mDNS code to service-connectivity-t

Instead of using a separate service-mdns library, move the code to
service-connectivity-t.

service-connectivity-t is chosen because it has access to hidden API of
classes that were made updatable in T, such as NsdServiceInfo and
NsdManager. mdns code can be there as it is only loaded on T+.

Bug: 241738458
Test: atest
Change-Id: I7eb6c9ab8bf0e0a614ea2994c6ed80a1a780241f
46 files changed