[llvm] [mlir] Allowing RDV to call `getArgOperandsMutable()` (PR #160415)

[Francisco Geiman Thiesen via llvm-commits]

FranciscoThiesen wrote:

> Can you split ADT changes to a separate PR and add unit tests?

I've split the ADT work into (https://github.com/llvm/llvm-project/pull/160726), could you please review @kuhar ?

https://github.com/llvm/llvm-project/pull/160415