RFR: 8294983: SSLEngine throws ClassCastException during handshake [v4]

[Kevin Driver]

> Fixes a scenario where a `ServerHandshakeContext` might be cast as a `ClientHandshakeContext`.

Kevin Driver has updated the pull request incrementally with one additional commit since the last revision:

  added explanatory comment

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13727/files
  - new: https://git.openjdk.org/jdk/pull/13727/files/0754990b..24956f70

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13727&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13727&range=02-03

  Stats: 6 lines in 1 file changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13727.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13727/head:pull/13727

PR: https://git.openjdk.org/jdk/pull/13727