RFR: 8317514: Ensure MemorySegment is initialized before touching NativeMemorySegmentImpl [v2]

[Maurizio Cimadamore]

> This PR makes sure that `MemorySegment` is initialized *before* any of its subclasses.
> This is done by centralizing all the memory segment factories in a single implementation class (`SegmentFactories`).
> Doing so addresses a possible deadlock condition when using multiple threads.

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  Address review comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16187/files
  - new: https://git.openjdk.org/jdk/pull/16187/files/2aad11cf..b9ad352b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16187&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16187&range=00-01

  Stats: 12 lines in 2 files changed: 0 ins; 11 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16187.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16187/head:pull/16187

PR: https://git.openjdk.org/jdk/pull/16187