RFR: 8304824: NMT should not use ThreadCritical [v2]

[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

Robert Toyonaga has updated the pull request incrementally with one additional commit since the last revision:

  Comments. Hide assertion behind DEBUG. Replace MemoryFileTracker locker. make reentrant.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20852/files
  - new: https://git.openjdk.org/jdk/pull/20852/files/97f8296f..38d440b8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20852&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20852&range=00-01

  Stats: 63 lines in 8 files changed: 31 ins; 20 del; 12 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