RFR: 8331195: Improve com.sun.net.httpserver.HttpExchange usability [v3]

[robert engels]

> improve the HttpExchange api with documented constants and convenience methods to avoid common bugs

robert engels has updated the pull request incrementally with one additional commit since the last revision:

  Update src/jdk.httpserver/share/classes/com/sun/net/httpserver/HttpExchange.java
  
  Co-authored-by: Michael McMahon <70538289+Michael-Mc-Mahon at users.noreply.github.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18955/files
  - new: https://git.openjdk.org/jdk/pull/18955/files/6bb8d511..3af58d0c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18955&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18955&range=01-02

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18955.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18955/head:pull/18955

PR: https://git.openjdk.org/jdk/pull/18955