(This rolls forward part of a previous change, now that jarjar was fixed
to not get very slow when the number of rules increases).

Autogenerate connectivity jarjar rules at build time, to avoid issues
with forgotten jarjar rules or hard-to-diagnose errors introduced by
incorrect rules.

This change causes all classes in framework-connectivity(-t) and
service-connectivity to be jarjared into android.net.connectivity, but
still avoids jarjaring classes in com.android.server as before, to keep
it small.
For many classes this differs from the original jarjar rule.

Notes on implementation:

 - connectivity-jarjar-rules now has a subset
   framework-connectivity-jarjar-rules containing only the rules
   necessary for framework-connectivity. This is necessary because
   framework-connectivity cannot depend on rules generated based on
   service-connectivity, as there would be a dependency cycle
   (service-connectivity depends on framework-connectivity); Soong even
   crashes with a stack overflow.

 - framework-wifi.stubs.module_lib is added to
   framework-connectivity-pre-jarjar as it is necessary to build it (it
   is already in impl_only_libs in the defaults).
   It is unclear why framework-connectivity-pre-jarjar could build
   before that (possibly because it was only used as "lib" ?)

 - Fix package-private visibility; for example NattSocketKeepalive,
   TcpSocketKeepalive are not API so should be jarjared, but are used
   by ConnectivityManager which is not jarjared, so they are not in the
   same package after the change. Package-private members in the
   former 2 need to be public to be accessible. Changes in this commit
   are all that is needed, as demonstrated by followup commits that move
   the classes to a different package without further changes, and that
   enforce that no class in an API package gets jarjared.

 - framework-connectivity-internal-test-defaults is separated from
   framework-connectivity-test-defaults, for unit tests that need to
   access internal jarjared classes. Such tests need to use the jarjar
   rules themselves too, so this is only appropriate for connectivity
   internal unit tests.

Test: atest ConnectivityCoverageTests CtsNetTestCases
Bug: 217129444
Change-Id: Ib1bd939b71c0171d945fc01b96195d2f620ff13b