[mlir] Rename arith.addi_carry to arith.addui_carry

The intention is to have this op lowered to
`llvm.intr.uadd.with.overflow` or `spv.IAddCarry`. LLVM has a second
intrinsic for signed add-with-overflow, `llvm.intr.sadd.with.overflow`,
with different semantics. Therefore we should have 2 ops with `arith`,
and be explicit about signed/unsigned semantics.

Rename `arith.addi_carry` to `arith.addui_carry` before we introduce a
signed version of this op: `arith.addsi_carry`.

Reviewed By: antiagainst

Differential Revision: https://reviews.llvm.org/D132491