Expose EthernetManager state and control APIs.

This CL exposes EthernetManager APIs that settings and other
system components can use to modify and monitor Ethernet state.
The new APIs are similar to the existing @hide methods but
pass on more information and meet API guidelines:

1. Add an InterfaceStateListener interface, and
   addInterfaceStateListener and removeInterfaceStateListener
   methods that meet API guidelines (e.g., take Executor, take
   SAM parameter last, etc.) This new listener passes interface
   state (absent, up, down), role (client or server) and IP
   configuration.
2. Implement the legacy Listener type as a subinterface of the
   new interface. Hopefully existing callers should be able to
   use it unchanged.
3. Expose setIncludeTestInterfaces as module-lib api instead of
   TestApi, since modules cannot expose TestApi methods.

Bug: 210586283
Test: m
Test: atest EthernetServiceTests
Test: atest EthernetTetheringTest
Change-Id: I88240a546ab51d128ed83775499f2bcabab74db0
Merged-In: I88240a546ab51d128ed83775499f2bcabab74db0