RFR: 8310428: Add CollectedHeap::reserved_range() API to return reserved heap memory range

[Ashutosh Mehra]

Please review this patch to add a new API `CollectedHeap::reserved_range()`. The changes are extracted out from https://github.com/openjdk/jdk/pull/14520 as per the suggestion [here](https://github.com/openjdk/jdk/pull/14520#discussion_r1234991165). Support for ZGC is not implemented yet as it can have discontiguous heap regions and unlike other collectors, it does not set `CollectedHeap::_reserved`.

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Commit messages:
 - 8310428: Add CollectedHeap::reserved_range() API to return reserved heap memory range

Changes: https://git.openjdk.org/jdk/pull/14595/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14595&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310428
  Stats: 41 lines in 14 files changed: 6 ins; 9 del; 26 mod
  Patch: https://git.openjdk.org/jdk/pull/14595.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14595/head:pull/14595

PR: https://git.openjdk.org/jdk/pull/14595