Dhruv Chopra

Marked as a draft because I need to confirm that a failure in the builds is not related to my changes, and some formatting changes need to be made.

FYI @r30shah @joransiu @zl-wang @ChengJin01 @0xdaryl

This commit should pass all up call tests found in @ChengJin01's branch: https://github.com/ChengJin01/openj9/find/jep389_419_ffi_upcall_v4_struct_v2_outofline_mh_v9_fin_v8 under the `test/functional/Java18andUp/src/org/openj9/test/jep419/upcall/` directory. Note however that the Memory Padding in `UpcallMHWithStructTests.java` is not compatible on zLinux....

I also did my own unit testing as I was building the solution to make sure I'm covering all cases. On zLinux the parameter can be stored in one of...

I did test the last time I pushed code changes to this branch a week or two ago. Just to be sure I'm doing a clean build and will test...

Merge conflicts resolved and all my local tests have passed as well.

> @dchopra001 going to take a look at the changes in details, but a quick question, would it be possible (and simpler as well) to common some of the instruction...

Adding the tests I used to verify correctness. This should provide confidence that the feature is complete. [UpcallMHWithPrimTests.java.txt](https://github.com/user-attachments/files/16168631/UpcallMHWithPrimTests.java.txt) I will do complete manual testing using the jtreg + jck +...

> @dchopra001 : Line Ending check is flagging the following -- Can you double check? The line endings check has passed now.

@joransiu If you have no more review comments, then would you be able to approve and launch the PR testing?