Conditional (ternary) operator support

Moved from https://github.com/UnitTestBot/UTBotCpp/issues/324

**Description**
Add conditional (ternary) operator ` ? : ` support.

**Current behavior**
Source code:
```cpp
int ternary_positive(int n) {
    int res = n >= 0 ? 1 : 0;
    return res;
}

```
Only one test generated

**Expected behavior** More tests generated.