RFR: 8366241: NMT: Consolidate [Virtual/Committed/Reserved]Regions into one structure

[Afshin Zafari]

The structures `CommittedMemoryRegion` and `ReservedMemoryRegion` are merged into the `VirtualMemoryRegion`.

Tests:
tiers1-5, main platforms, debug/product

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Commit messages:
 - 8366241: NMT: Consolidate [Virtual/Committed/Reserved]Regions into one structure

Changes: https://git.openjdk.org/jdk/pull/27137/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27137&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366241
  Stats: 195 lines in 12 files changed: 38 ins; 93 del; 64 mod
  Patch: https://git.openjdk.org/jdk/pull/27137.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27137/head:pull/27137

PR: https://git.openjdk.org/jdk/pull/27137