[llvm] [SandboxIR] Implement Instruction flags (PR #103343)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

> > actually, I think the Instruction version of some of these methods are not widely used, only the FPMathOperator versions. we might be able to do some cleanup and remove these from Instruction
> 
> So how should we proceed? Shall I stash this until we do the cleanup?

hmm it's kind of annoying to untangle given the LLVM class hierarchy. go ahead with this change, I'm giving up on refactoring this for now

https://github.com/llvm/llvm-project/pull/103343