Use public APIs instead of Conscrypt ones

Use the equivalent public APIs on SSLContext instead of reaching into
OpenSSLContextImpl, except for the one place where a
Conscrypt-specific API is needed.

Bug: 123738844
Bug: 119752589
Test: cts -m CtsLibcoreTestCases
Change-Id: Idcf258b980b4c37fbe1166b4189454d6a5c35c83
1 file changed