[foreign-memaccess+abi] RFR: Modernize code [v4]

[Per Minborg]

On Mon, 25 Sep 2023 10:16:01 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This PR proposes to modernize some parts of the code with constructs from newer Java versions.
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove the use of Unsafe

src/java.base/share/classes/jdk/internal/foreign/HeapMemorySegmentImpl.java line 89:

> 87:         }
> 88:         JavaNioAccess nioAccess = SharedSecrets.getJavaNioAccess();
> 89:         return nioAccess.newHeapByteBuffer(baseByte, (int)offset - Utils.BaseAndScale.BYTE.base(), (int) byteSize(), null);

As records instance variables are trusted to be constant, this still allows for inlining and constant folding.

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PR Review Comment: https://git.openjdk.org/panama-foreign/pull/894#discussion_r1335684454