RFR: 7105350: HttpExchange's attributes are the same as HttpContext's attributes

[Josiah Noel]

Now ExchangeImpl will default to having a separate attribute map for the request duration.

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Commit messages:
 - Merge branch 'openjdk:master' into JDK-7105350
 - Separate attributes for exchangeImpl

Changes: https://git.openjdk.org/jdk/pull/27652/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27652&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-7105350
  Stats: 19 lines in 1 file changed: 7 ins; 6 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/27652.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27652/head:pull/27652

PR: https://git.openjdk.org/jdk/pull/27652