RFR: 8334137: Marlin: replace sun.misc.Unsafe memory access methods with FFM

[Per Minborg]

On Tue, 10 Jun 2025 17:51:02 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

> If there is no performance penalty for accessing data from a memory segment created using the global arena, then we could switch to that for JavaFX as well.

Using memory from the Global arena can actually be _faster_ as we do not have to perform any liveness checks for such segments. So, I think this is a good move. Also, the memory does not have to be acquired/released if the address is conveyed to native code (as the segment's scope never closes).

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PR Comment: https://git.openjdk.org/jfx/pull/1814#issuecomment-2961322752