[InstCombine] Missed: `trunc(((X << m) + C) >> k) -> trunc((X << (m - k)) + (C >> k))`

Missed optimization

```llvm
define i8 @src(i32 %x) local_unnamed_addr #0 {
%v2 = shl i32 %x, 12
%v3 = add i32 %v2, 34816
%v16 = lshr i32 %v3, 8
%v17 = trunc i32 %v16 to i8
ret i8 %v17
}

define i8 @tgt(i32 %x) local_unnamed_addr {
%v2 = shl i32 %x, 4
%v3 = add i32 %v2, 136
%v4 = trunc i32 %v3 to i8
ret i8 %v4
}
```

https://alive2.llvm.org/ce/z/Q4xYvT

Extracted from zlib_deflate function in deflate