[mlir][math] Add `math.absi` op

Adds an integer absolute value op to the math dialect.

When converting to LLVM, this op is lowered to the LLVM `abs` intrinsic.
When converting to SPIRV, this op is lowered to `spv.GL.SAbs`.

Depends on D131325

Reviewed By: ftynse

Differential Revision: https://reviews.llvm.org/D131327