RFR: 8345656: Move os alignment functions out of ReservedSpace

[Stefan Karlsson]

I have a wish to simplify the ReservedSpace classes (See: [JDK-8345655](https://bugs.openjdk.org/browse/JDK-8345655)) and as a small step I would like to move the small helper functions that align addresses and sizes to `os::vm_page_size()` and `os::vm_allocation_granularity()` out to be `os::` helpers.

Tested tier1-3 together with the other patches in the JDK-8345655 prototype.

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Commit messages:
 - 8345656: Move os alignment functions out of ReservedSpace

Changes: https://git.openjdk.org/jdk/pull/22600/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22600&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345656
  Stats: 59 lines in 12 files changed: 29 ins; 15 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/22600.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22600/head:pull/22600

PR: https://git.openjdk.org/jdk/pull/22600