ssl: make DistinguishedNameParser a package-private class in org.apache.http.conn.ssl

Needed by AbstractVerifier, needed by framework/base

DistinguishedNameParser taken from libcore, commit a5c16db453098d7ab945edd379a

This commit was adapted from commit 50dc0c27ff00bfd82fb9cce1c86312efa550170f

Not cherrypicking from dev branch as the original CL to do it went wrong
and would need to cherrypick more changes

Change-Id: I1c282b731c778a79775d9d54b7b7d7223d84397d