Recommit "[SCCP] Use range info to prove AddInst has NUW flag."

This reverts commit 531756b9.

The recommitted version fixes a crash when one of the operands is a
constant other than a ConstantInt. Test for that case have been added
in 5b16cd97.

It splits off the new logic into a separate function because setting the
flags is quite different compared to the other cases handled in replaceSignedInst
which all require replacing an existing instruction.

It also guards makeGuaranteedNoWrapRegion by `if (!Inst.hasNoUnsignedWrap())`
as discussed in the review.

Fixes #60280.
Fixes #60278.

Original message:
    This patch updates SCCP to use the value ranges of AddInst operands to
    try to prove the AddInst does not overflow in the unsigned sense and
    adds the NUW flag. The reasoning is done with
    makeGuaranteedNoWrapRegion (thanks @nikic for point it out!).

    Follow-ups will include adding NSW and extension to more
    OverflowingBinaryOperators.

    Reviewed By: nikic

    Differential Revision: https://reviews.llvm.org/D142387