RFR: 8377396: GenShen: Consolidate and simplify in place region promotions [v3]

[Aleksey Shipilev]

On Wed, 11 Feb 2026 18:43:06 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> The logic to select and execute in place region promotions is spread out across different files. This is a mechanical refactoring to simplify the code and encapsulate the abstraction.
>
> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add new line

Marked as reviewed by shade (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/29618#pullrequestreview-3786716486