RFR: 8234502: Merge GenCollectedHeap and SerialHeap [v12]

[Chris Plummer]

On Thu, 11 Jan 2024 15:46:45 GMT, Lei Zaakjyu <duke at openjdk.org> wrote:

>> 8234502: Merge GenCollectedHeap and SerialHeap
>
> Lei Zaakjyu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   restore and rename 'GenCollectedHeap' to 'SerialHeap'

Sorry about the false alarms. Not noticing that vmStructs_serial.hpp was also updated threw me off. The changes look fine. I ran the SA tests locally and they passed.

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Marked as reviewed by cjplummer (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/16927#pullrequestreview-1816739658