RFR: 8366658: Add missing locks when accessing the VirtualMemoryTracker instance in tests and MemMapPrinter [v2]

[Johan Sjölen]

> Hi,
> 
> This PR adds the missing locks for the tests and MemMapPrinter, also fixes a small bug in `walk_virtual_memory`. See inline review comments.
> 
> Passes tier1.

Johan Sjölen has updated the pull request incrementally with one additional commit since the last revision:

  Update src/hotspot/share/nmt/virtualMemoryTracker.hpp
  
  Co-authored-by: David Holmes <62092539+dholmes-ora at users.noreply.github.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27038/files
  - new: https://git.openjdk.org/jdk/pull/27038/files/20d2f5de..1cb83538

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27038&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27038&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27038.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27038/head:pull/27038

PR: https://git.openjdk.org/jdk/pull/27038