[InstCombine] Simplify nested selects with implied condition (#83739)

This patch does the following simplification:
```
sel1 = select cond1, X, Y 
sel2 = select cond2, sel1, Z
-->
sel2 = select cond2, X, Z if cond2 implies cond1
sel2 = select cond2, Y, Z if cond2 implies !cond1
```
Alive2: https://alive2.llvm.org/ce/z/9A_arU

It cannot be done in CVP/SCCP since we should guarantee that `cond2` is
not an undef.