RFR: 8349146: [REDO] Implement a better allocator for downcalls

[Per Minborg]

On Wed, 23 Apr 2025 14:05:58 GMT, Per Minborg <pminborg at openjdk.org> wrote:

> This PR is based on the work of @mernst-github and aims to implement an _internal_ thread-local 'stack' allocator, which works like a dynamically sized arena, but with reset functionality to reset the allocated size back to a certain level. The underlying memory could stay around between calls, which could improve performance.
> 
> Re-allocated segments are not zeroed between allocations.

> We can not just re-use the original test due to: https://bugs.openjdk.org/browse/JDK-8350455
> 
> See my comment here: [#23142 (comment)](https://github.com/openjdk/jdk/pull/23142#issuecomment-2673194510)

I ran the test 250 times on my Mac machine (macOS 15.4.1)with no problems but, maybe we should problem list or exclude macOS testing?

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PR Comment: https://git.openjdk.org/jdk/pull/24829#issuecomment-2840083043