RFR: 8304824: NMT should not use ThreadCritical

[Robert Toyonaga]

### Summary
This PR just replaces `ThreadCritical` with a lock specific to NMT.  `ThreadCritical` is a big lock and is unnecessary for the purposes of NMT. I've implemented the new lock with a semaphore so that it can be used early before VM init.  There is also the possibility of adding assertions in places we expect NMT to have synchronization. I haven't added assertions yet in many places because some code paths such as the (NMT tests)  don't lock yet. I think it makes sense to close any gaps in locking in another PR in which I can also add more assertions. 

Testing:
- hotspot_nmt
- gtest:VirtualSpace
- tier1

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Commit messages:
 - Replace ThreadCritical with a specific NMT lock

Changes: https://git.openjdk.org/jdk/pull/20852/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20852&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304824
  Stats: 58 lines in 10 files changed: 35 ins; 4 del; 19 mod
  Patch: https://git.openjdk.org/jdk/pull/20852.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20852/head:pull/20852

PR: https://git.openjdk.org/jdk/pull/20852