RFR: 8234502: Merge GenCollectedHeap and SerialHeap [v12]

[Albert Mingkun Yang]

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'

Tier1-6 pass.

I used `git diff --color-moved=dimmed_zebra <old> <new>` to check the change inside hotspot and it's mostly code-moving, as expected. There are some still format issues (header include order and broken indentation), which can probably be fixed in followup PRs.

-------------

Marked as reviewed by ayang (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/16927#pullrequestreview-1817728332