RFR: 8235786: Javadoc for com/sun/net/httpserver/HttpExchange.java#setAttribute is unclear [v3]

[Jaikiran Pai]

> Can I please get a review of this doc-only change which proposes to clarify the behaviour of `com.sun.net.httpserver.HttpExchange.setAttribute()` and `com.sun.net.httpserver.HttpExchange.getAttribute()` methods?
> 
> As noted in https://bugs.openjdk.org/browse/JDK-8235786, it's not clear from the javadoc of these methods that the attributes that are set or retrieved through the exchange are actually those that belong to the entire `com.sun.net.httpserver.HttpContext` and thus are shared by all exchanges.
> 
> The commit in this PR specifies this behaviour to match the current implementation. I'll file a CSR once we settle on the text.

Jaikiran Pai has updated the pull request incrementally with one additional commit since the last revision:

  update an existing test to verify HttpExchange.getAttribute()/setAttribute()

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/22454/files
  - new: https://git.openjdk.org/jdk/pull/22454/files/6628c51d..3123c33c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22454&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22454&range=01-02

  Stats: 118 lines in 1 file changed: 101 ins; 5 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/22454.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22454/head:pull/22454

PR: https://git.openjdk.org/jdk/pull/22454