RFR: 8345655: Move reservation code out of ReservedSpace [v2]

[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:

Stefan Karlsson has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Merge remote-tracking branch 'upstream/master' into reserved_space_rewrite
 - Fix comment
 - 8345655: Move reservation code out of ReservedSpace

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Changes: https://git.openjdk.org/jdk/pull/22712/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22712&range=01
  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