RFR: 8281210: Add manpage changes for PAC-RET protection on Linux/AArch64

[David Holmes]

Please review this trivial update to apply the manpage changes from JDK-8277204. Those changes had to be applied to the closed markdown sources and then the regenerated output brought back into OpenJDK. There are some minor formatting changes to suit the prevailing style of the runtime flags section, and some incidental line break differences introduced by the pandoc tool.

Thanks,
David

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Commit messages:
 - 8281210: Add manpage changes for PAC-RET protection on Linux/AArch64

Changes: https://git.openjdk.java.net/jdk/pull/7641/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7641&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281210
  Stats: 23 lines in 1 file changed: 7 ins; 2 del; 14 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7641.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7641/head:pull/7641

PR: https://git.openjdk.java.net/jdk/pull/7641