ReduceOperands: Do not crash on vector of pointer types

Avoid crash in `reduceOperandsOneDeltaPass` function for operands with
vector of pointer type.

While on it add a `reduce-operands-ptr.ll` test in the spirit of the
existing `reduce-operands-int.ll`/`reduce-operands-fp.ll` tests.

Differential Revision: https://reviews.llvm.org/D135307