Fix HandleTableBucket::Contains to account for slots in DATAS

[hoyosjs]

This fixes iteration of the handle table for a given bucket. This bug had hit the DAC iteration as well as this code path. Each bucket has a handle table that has as many slots as cores for server GC. This was 1:1 prior to DATAs by default - it also hd a bug when an explicit number of heaps was set. The only reason this hadn't had any issues prior to this is this function is unused.

The other option is to use the first commit in this PR - rev the major of the GC interface and delete the function altogether.

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[Copilot]

Pull request overview

This PR fixes handle table bucket membership checks in CoreCLR GC by ensuring HandleTableBucket::Contains iterates over the actual number of handle-table slots allocated per bucket (which can differ from IGCHeap::GetNumberOfHeaps() in some configurations, e.g., with DATAs / explicit heap counts).

Changes:

• Update HandleTableBucket::Contains to iterate using getNumberOfSlots() rather than g_theGCHeap->GetNumberOfHeaps().
• Store the slot count in a local n_slots to match surrounding patterns and avoid repeated queries.

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