RFR: 8281236: (D)TLS key exchange named groups [v5]

[Xue-Lei Andrew Fan]

> This update is to support key exchange named groups customization for individual (D)TLS connection. Please review the CSR as well:
> CSR: https://bugs.openjdk.org/browse/JDK-8291950
> RFE: https://bugs.openjdk.org/browse/JDK-8281236
> Release-note: https://bugs.openjdk.org/browse/JDK-8291975
> 
> This is an effort similar to [JDK-8280494: "(D)TLS signature schemes"](https://bugs.openjdk.org/browse/JDK-8280494)

Xue-Lei Andrew Fan has updated the pull request incrementally with one additional commit since the last revision:

  review feedback update

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/9776/files
  - new: https://git.openjdk.org/jdk/pull/9776/files/2039c113..21bf18be

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9776&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9776&range=03-04

  Stats: 29 lines in 5 files changed: 19 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/9776.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9776/head:pull/9776

PR: https://git.openjdk.org/jdk/pull/9776