8383864: G1: Separate worker-local refinement data from shared concurrent refinement stats

[albertnetymk]

This change adds a plain G1RefineData for worker-local refinement counters and has G1ConcurrentRefineStats atomically aggregate that data at the end of each worker task. Sweep and yield timing remain accounted directly in the shared stats.

Test: tier1

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• JDK-8383864: G1: Separate worker-local refinement data from shared concurrent refinement stats (Enhancement - P4)

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