Use public API for Conscrypt features

Historically, extra Conscrypt features were enabled by calling hidden
APIs.  We now have public APIs for these, so use those instead.
Continue calling the non-public APIs in most cases because older
versions of Conscrypt may be bundled with apps and third-party
SSLSocket providers may have taken advantage of our duck-typing to
enable compatibility with these features, but never call them when
dealing with a platform socket to ensure we can't break this with
Conscrypt module updates.

In future, we want to depend on Conscrypt stubs instead, but those
don't exist yet.  b/129126571 tracks that work.

Test: cts -m CtsLibcoreTestCases
Test: cts -m CtsLibcoreOkHttpTestCases
Bug: 128280837
Change-Id: Id5a04a14ebe9737a85d3347a230132c151e1ec5a