[jdk18] RFR: 8280441: "classpath exception" in several files from jdk.httpserver

[Julia Boes]

This change adds the classpath exception to the copyright header of the files in question. As source files, they should have both the GPL and the classpath exception.

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Commit messages:
 - initial commit

Changes: https://git.openjdk.java.net/jdk18/pull/111/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18&pr=111&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280441
  Stats: 28 lines in 7 files changed: 14 ins; 0 del; 14 mod
  Patch: https://git.openjdk.java.net/jdk18/pull/111.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18 pull/111/head:pull/111

PR: https://git.openjdk.java.net/jdk18/pull/111