[8u] RFR: 8206925: Support the certificate_authorities extension

[Severin Gehwolf]

Hi,

Please review this OpenJDK 8u backport of the certificate_authorities
extensionj. The OpenJDK 11u patch didn't apply cleanly after path
unshuffeling, but was fairly trivial to resolve. Conflicts caused by:

1. X509Authentication.java copyright line conflict only. Resolved
   manually.
2. SSLContextTemplate.java private interface methods not allowed in
   JDK 8. It's a JDK 9+ feature via JEP 213. Changed modifier to
   default. Note: this is code used in tests only.
3. TooManyCAs.java. Added -Djdk.tls.client.protocols=TLSv1.3 to the
   test invocations since JDK 8u doesn't enable TLSv1.3 on the
   client side by default. See JDK-8248721, CSR of the TLSv1.3 8u
   backport.

Other than that, the patch is identical to the OpenJDK 11.0.12 version
of this patch.

This introduces a new system property,
jdk.tls.client.enableCAExtension, for compatibilty reasons. CSR has
been reused from the Oracle JDK backport. See below.

Bug: https://bugs.openjdk.java.net/browse/JDK-8206925
CSR: https://bugs.openjdk.java.net/browse/JDK-8248709
webrev: https://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8206925/jdk8/02/webrev/

Testing: sun/security/ssl tests and tier1. No new regressions.
         New tests pass.

Thoughts?

Thanks,
Severin