RFR: 8362276: NMT tests should have locks for the entire tests [v2]

[Gerard Ziemski]

> We restructure the code to make sure we cover the code that uses the global tree instance (but nothing else that uses the same lock internally) as needed:
> 
> - we move MemoryReserver::reserve() to the top to do as the first thing
> - we grab the MemTracker::NmtVirtualMemoryLocker nvml
> - do all the usual test stuff, including checking, which grabs the global instance of the tree
> - we move remove_all() to the very bottom to do as the last thing
> 
> Testing: runnig Mach5 tier1-4 right now...

Gerard Ziemski has updated the pull request incrementally with one additional commit since the last revision:

  restructure code to make sure we use the lock as needed

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/26324/files
  - new: https://git.openjdk.org/jdk/pull/26324/files/4958be33..4387bee2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26324&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26324&range=00-01

  Stats: 38 lines in 1 file changed: 20 ins; 18 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/26324.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26324/head:pull/26324

PR: https://git.openjdk.org/jdk/pull/26324