[ValueTracking] Let propagatesPoison support binops/unaryops/cast/etc.

Summary:
This patch makes propagatesPoison be more accurate by returning true on
more bin ops/unary ops/casts/etc.

The changed test in ScalarEvolution/nsw.ll was introduced by
https://github.com/llvm/llvm-project/commit/a19edc4d15b0dae0210b90615775edd76f021008 .
IIUC, the goal of the tests is to show that iv.inc's SCEV expression still has
no-overflow flags even if the loop isn't in the wanted form.
It becomes more accurate with this patch, so think this is okay.

Reviewers: spatel, lebedev.ri, jdoerfert, reames, nikic, sanjoy

Reviewed By: spatel, nikic

Subscribers: regehr, nlopes, efriedma, fhahn, javed.absar, llvm-commits, hiraditya

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78615