[jdk21u-dev] RFR: 8326524: Rename agent_common.h

[Goetz Lindenmaier]

I backport this to keep tests up to date.

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Commit messages:
 - Backport d482c1af28cacd60cc05fe3f975a00a0c68c72b7

Changes: https://git.openjdk.org/jdk21u-dev/pull/1781/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1781&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326524
  Stats: 551 lines in 547 files changed: 0 ins; 0 del; 551 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1781.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1781/head:pull/1781

PR: https://git.openjdk.org/jdk21u-dev/pull/1781