RFR: 8230623: Extract command-line help for -Xlint sub-options to new --help-lint

[Guoxiong Li]

Hi all,

This patch splits out the concrete keys of -Xlint into a new option, --help-lint, 
so that the output of --help-extra is kept clean and concise.

Thank you for taking the time to review.

Best Regards.

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Commit messages:
 - 8230623: Extract command-line help for -Xlint sub-options to new --help-lint

Changes: https://git.openjdk.java.net/jdk/pull/1758/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1758&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8230623
  Stats: 64 lines in 5 files changed: 37 ins; 22 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1758.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1758/head:pull/1758

PR: https://git.openjdk.java.net/jdk/pull/1758