RFR: 8329840: Fix ZPhysicalMemorySegment::_end type

[Axel Boldt-Christmas]

`ZPhysicalMemorySegment::_end` should use `zoffset_end` for its type instead of `zoffset`.

Starting a debug vm with a 16TB min heap size will crash with an invalid `zoffset` assert.

Testing with ZGC tier1-tier7 on linux x64+aarch64

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Commit messages:
 - 8329840: Fix ZPhysicalMemorySegment::_end type

Changes: https://git.openjdk.org/jdk/pull/18673/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18673&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329840
  Stats: 54 lines in 4 files changed: 49 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/18673.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18673/head:pull/18673

PR: https://git.openjdk.org/jdk/pull/18673