RFR: 8345655: Move reservation code out of ReservedSpace

[Stefan Karlsson]

The ReservedSpace class and its friends has a dual functionality of describing a reserved memory region AND it also reserves memory. I would like to split this so that the ReservedSpace classes only acts as data carrier about reserved memory and then have a more explicit API for reserving memory and baking a ReservedSpace given the outcome of the reservation.

See the first comment for the full description:

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Commit messages:
 - 8345655: Move reservation code out of ReservedSpace

Changes: https://git.openjdk.org/jdk/pull/22712/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22712&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345655
  Stats: 2107 lines in 59 files changed: 1182 ins; 806 del; 119 mod
  Patch: https://git.openjdk.org/jdk/pull/22712.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22712/head:pull/22712

PR: https://git.openjdk.org/jdk/pull/22712