RFR: 8369913: Parallel: Refactor PSAdjustTask

[Francesco Andreuzzi]

On Wed, 15 Oct 2025 13:31:06 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Cleanup roots processing (adjusting/remapping) during the adjust-phase of full-gc, so that relevant roots are grouped together with some documentations. Also, the use of `SubTasksDone` is replaced with a `volatile bool`, which is more transparent in the context.
> 
> Test: tier1-5

Marked as reviewed by fandreuzzi (Author).

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PR Review: https://git.openjdk.org/jdk/pull/27822#pullrequestreview-3403614554