[InstCombine] Fold more select of selects using isImpliedCondition

This is a simple folding that does these:

```
select x_inv, true, (select y, x, false)
=>
select x_inv, true, y
```
https://alive2.llvm.org/ce/z/-STJ2d

```
select (select y, x, false), true, x_inv
=>
select y, true, x_inv
```
https://alive2.llvm.org/ce/z/6ruYt6

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D101807