[SECV] Try to push the op into ZExt: A + zext (-A + B) -> zext (B) (#151227)

Try to push the constant operand into a ZExt:
A + zext (-A + B) -> zext (B), if trunc (A) + -A + B does not
unsigned-wrap.

The actual code supports ZExts with arbitrary number of arguments, hence
the getAddExpr in the return.

This helps SCEV reasoning in some cases, commonly when adding an offset
to a zero-extended SCEV that subtracts the same offset.

Note that this is restricted to cases where we can fold away an operand
of the inner Add. This is needed to avoid bad interactions with patterns
when forming ZExts, which try to push to ZExt to add operands.

https://alive2.llvm.org/ce/z/q7d303

PR: https://github.com/llvm/llvm-project/pull/151227

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