[llvm] [SandboxIR] Implement StoreInst (PR #99707)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

I have two jokes:
A MemoryAccessBase for LoadInst and StoreInst with:
```
 Value *getPointerOperand() const;
  Align getAlign() const { return cast<llvm::StoreInst>(Val)->getAlign(); }
  bool isSimple() const { return cast<llvm::StoreInst>(Val)->isSimple(); }
  bool isUnordered() const { return cast<llvm::StoreInst>(Val)->isUnordered(); }
```

Second joke: Instructions.h to split them out of SandboxIR.h

https://github.com/llvm/llvm-project/pull/99707