Implement safe API for operand bundles manipulation

[airwoodix]

Operand bundles can be attached to call and invoke instructions. Starting with LLVM18, llvm-sys exposes the relevant bindings for building instructions with attached operand bundles, as well as parsing operand bundles from those instructions.

I have a prototype implementation of a safe API here: https://github.com/TheDan64/inkwell/compare/master...airwoodix:inkwell:get-operand-bundles

Would you consider a PR upstreaming such changes?

[TheDan64]

Sure, would be happy to review a PR