Setup NativeTestServer

this adds the classes dependent on the nativetestserverThis adds the classes dependent on the nativetestserver.

This setup depends on the cronet's platform implementation.
However, the tests jnilib is not prefixed and
because of that:
- We don't jarjar the base classes
- Don't jar the test classes
since the .so file needs the unjarjared versions.

Test: atest NetHttpTestServer
Bug: 267353182
Change-Id: Id5cfc8f842df4b13cef6f56dbaa6b9563c3989de