Reapply [CVP] Simplify non-overflowing saturating add/sub

If we can determine that a saturating add/sub will not overflow based
on range analysis, convert it into a simple binary operation. This is
a sibling transform to the existing with.overflow handling.

Reapplying this with an additional check that the saturating intrinsic
has integer type, as LVI currently does not support vector types.

Differential Revision: https://reviews.llvm.org/D62703

llvm-svn: 362263