[jdk17u-dev] RFR: 8322321: Add man page doc for -XX:+VerifySharedSpaces

[Jonathan Dowland]

This is an unclean backport of a manpage fix, for Oracle parity. The conflict was trivial to resolve manually and was due to the troff source being updated post-17u for 8297164, which is unlikely to be backported itself.

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Commit messages:
 - 8322321: Add man page doc for -XX:+VerifySharedSpaces

Changes: https://git.openjdk.org/jdk17u-dev/pull/2098/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=2098&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322321
  Stats: 9 lines in 1 file changed: 9 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/2098.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/2098/head:pull/2098

PR: https://git.openjdk.org/jdk17u-dev/pull/2098