Support if function syntax: IF( condition, [value_if_true], [value_if_false] )

[段雄]

Hi all, I use calcite find can't handle if function well.
```
 No match found for function signature IF(<BOOLEAN>, <CHARACTER>,
<CHARACTER>) (state=,code=0)
```

So I want to add support this function in calcite, If you agree with this view.
I will create an issue and work on. Thank you very much.