RFR: 8367422: Parallel: Refactor local variables names in copy_unmarked_to_survivor_space

[Thomas Schatzl]

On Thu, 11 Sep 2025 13:59:20 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Trivial "renaming" a local variable and its type to better reflect its semantic and avoid much `HeapWord*`-vs-`oop` conversion.
> 
> Test: Comparing the generated asm in release build and they are identical.

Marked as reviewed by tschatzl (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/27227#pullrequestreview-3223219013