[InstCombine] refactor visitOr() to use foldCastedBitwiseLogic()

Note: The 'and' case in foldCastedBitwiseLogic() is inheriting one extra
check from the nearly identical 'or' case:
  if ((!isa<ICmpInst>(Cast0Src) || !isa<ICmpInst>(Cast1Src))

But I'm not sure how to expose that difference in a regression test. 
Without that check, the 'or' path will infinite loop on:
test/Transforms/InstCombine/zext-or-icmp.ll
because the zext-or-icmp fold is attempting a reverse transform.

The refactoring should extend to the 'xor' case next to solve part of
PR26702.

llvm-svn: 261707