RFR: 8358483: G1: Remove G1HeapRegionManager::num_available_regions

[Ivan Walulya]

On Tue, 3 Jun 2025 09:10:28 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Simple cleanup of moving an API from `G1HeapRegionManager` to `G1CollectedHeap`.
> 
> Test: tier1

I would advocate for moving more APIs into `G1HeapRegionManager` instead of adding more to `G1CollectedHeap`.

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PR Comment: https://git.openjdk.org/jdk/pull/25611#issuecomment-2940101833