RFR: 8351216: ZGC: Store NUMA node count

[Joel Sikström]

To avoid calling into `os::Linux::max_numa_node()` and in turn libnuma on every count lookup, I propose we instead store the count statically inside ZNUMA. This is perfectly fine since the value that we get from libnuma is configured once during initialization and never change during runtime.

The count is set during platform dependent initialization and the getter is now defined in the common code in ZNUMA.cpp. On operating systems that ZGC does not support NUMA for (BSD and Windows) we keep the current behavior by setting the count to 1.

This is also preparation work for the Mapped Cache ([JDK-8350441](https://bugs.openjdk.org/browse/JDK-8350441)).

Testing:
* Tiers 1-3
* GHA
* Verify that the count is set on a Linux system with NUMA hardware

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Commit messages:
 - 8351216: Store NUMA node count

Changes: https://git.openjdk.org/jdk/pull/23922/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23922&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351216
  Stats: 28 lines in 7 files changed: 8 ins; 13 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/23922.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23922/head:pull/23922

PR: https://git.openjdk.org/jdk/pull/23922