RFR: 8310993: Missing @since tags in jdk.attach

[Kevin Walls]

Simple since tag addition in selected files.

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Commit messages:
 - 8310993: Missing @since tags in jdk.attach

Changes: https://git.openjdk.org/jdk/pull/14724/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14724&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310993
  Stats: 11 lines in 4 files changed: 7 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/14724.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14724/head:pull/14724

PR: https://git.openjdk.org/jdk/pull/14724