RFR: 7105350: HttpExchange's attributes are the same as HttpContext's attributes [v2]

[Josiah Noel]

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

Josiah Noel has updated the pull request incrementally with one additional commit since the last revision:

  require non null

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27652/files
  - new: https://git.openjdk.org/jdk/pull/27652/files/a1f2873c..62937b8b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27652&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27652&range=00-01

  Stats: 9 lines in 1 file changed: 0 ins; 5 del; 4 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