[InstCombine] C0 <<{nsw, nuw} (X - C1) --> (C0 >> C1) << X (2nd try)

The first attempt at this missed a check to make sure the offset
constant was in range and caused many bot failures.

That was missed in the Alive2 proof because on overshift creates
poison rather than the assert from APInt. Here's an alternate
attempt at a proof using count-trailing-zeros:
https://alive2.llvm.org/ce/z/pnXQYR

Original commit message:

This is similar to an existing pre-shift-of-constant fold:
8a9c70fc
...but in this case, we need no-wrap on the shl and a negative
offset:
https://alive2.llvm.org/ce/z/_RVz99