[LV] Use lookThroughAnd with logical reductions

If a reduction Phi has a single user which `AND`s the Phi with a type mask,
`lookThroughAnd` will return the user of the Phi and the narrower type represented
by the mask. Currently this is only used for arithmetic reductions, whereas loops
containing logical reductions will create a reduction intrinsic using the widened
type, for example:

  for.body:
    %phi = phi i32 [ %and, %for.body ], [ 255, %entry ]
    %mask = and i32 %phi, 255
    %gep = getelementptr inbounds i8, i8* %ptr, i32 %iv
    %load = load i8, i8* %gep
    %ext = zext i8 %load to i32
    %and = and i32 %mask, %ext
    ...

^ this will generate an and reduction intrinsic such as the following:
    call i32 @llvm.vector.reduce.and.v8i32(<8 x i32>...)

The same example for an add instruction would create an intrinsic of type i8:
    call i8 @llvm.vector.reduce.add.v8i8(<8 x i8>...)

This patch changes AddReductionVar to call lookThroughAnd for other integer
reductions, allowing loops similar to the example above with reductions such
as and, or & xor to vectorize.

Reviewed By: david-arm, dmgreen

Differential Revision: https://reviews.llvm.org/D105632

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