[jdk17u-dev] RFR: 8326728: Copyright header is missing

[Amit Kumar]

This PR adds the missing CE & GPL header in `src/jdk.incubator.foreign/share/classes/jdk/internal/foreign/ArenaAllocator.java` file.

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Commit messages:
 - adds GPL & CE

Changes: https://git.openjdk.org/jdk17u-dev/pull/2241/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=2241&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326728
  Stats: 25 lines in 1 file changed: 25 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/2241.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/2241/head:pull/2241

PR: https://git.openjdk.org/jdk17u-dev/pull/2241