jextract: Implement support for the custom plus operator

[AmrDeveloper]

Add support for the custom plus operator + to FFM and JNI

Issue #817

[ktoso]

Thank you @AmrDeveloper but @AbdAlRahmanGad is working on operators as part of the Swift Mentorship Program, so I'd like to ask you to find another topic to work on while we focus on a holistic operators solution with AbdAl 🙏

[ktoso]

I'll close this to avoid confusion, but I look forward to other contributions from you, thanks in advance! Hope this makes sense, cheers :)

[AmrDeveloper]

Thank you @AmrDeveloper but @AbdAlRahmanGad is working on operators as part of the Swift Mentorship Program, so I'd like to ask you to find another topic to work on while we focus on a holistic operators solution with AbdAl 🙏

Sorry for the confusion; I just found the issue is not assigned to anyone :D, and also no one commented that he is working on it, but it makes sense to close it. I will focus on support all other functional interfaces if no one is working on it

[ktoso]

We can't assign issues to non members of the project, but yes a comment would have been good. Sorry about that, and yes, finishing up the functional interfaces will be neat

[AmrDeveloper]

We can't assign issues to non members of the project, but yes a comment would have been good. Sorry about that, and yes, finishing up the functional interfaces will be neat

@ktoso Thank you. I will do that.

Good luck @AbdAlRahmanGad 🥳