RFR: 8318962: Javadoc: Update ProcessTools after suggestions in 8315097

[Leo Korinth]

Updates to javadoc after improvement ideas in the review of 8315097. I have also removed the incomplete invocation command line. I also removed incomplete information in `executeTestJvm` and added a link to `createLimitedTestJavaProcessBuilder`

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Commit messages:
 - 8318962: Javadoc: Update ProcessTools after suggestions in 8315097

Changes: https://git.openjdk.org/jdk/pull/16430/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16430&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318962
  Stats: 70 lines in 1 file changed: 42 ins; 4 del; 24 mod
  Patch: https://git.openjdk.org/jdk/pull/16430.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16430/head:pull/16430

PR: https://git.openjdk.org/jdk/pull/16430