New API for using HttpURLConnectionFactory and Dns

- Create a wrapper class which can refer to internal okhttp APIs.
- Add okhttp_impl_files to core-all in order to break the dependency
cycle where okhttp depends on core-all to build and core-all depends on
okhttp.

Bug: 182238821
Test: m update-api
Change-Id: Ibcb7b0e085119e28e8fb38f847fd2375199ba3c5
7 files changed