[jdk15u-dev] RFR: 8279505: Update documentation for RETRY_COUNT and REPEAT_COUNT

[Yuri Nesterenko]

Document(-only) change is applicable to 15u, too, and should be backported.

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Commit messages:
 - Backport bc12381105ef5ba14f99304a220817e97c9a99b5

Changes: https://git.openjdk.org/jdk15u-dev/pull/219/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk15u-dev&pr=219&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8279505
  Stats: 8 lines in 2 files changed: 4 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk15u-dev/pull/219.diff
  Fetch: git fetch https://git.openjdk.org/jdk15u-dev pull/219/head:pull/219

PR: https://git.openjdk.org/jdk15u-dev/pull/219