Proposal: Add Exit If to VB

Will be useful for quick exit and enable to avoid 'iffize' inactive code

First case:

```
...
If x = 0 Then
Dim y = 0
...
If y > 1 Then Exit If
...
End If
```

Here Exit If exits from outer If

Second case:

```
...
If x = 0 Then
...
Exit If
...
...
End If
```

Seems like unnecessary, but this is useful when we want to temporarily avoid some code (potentially problematic) from execution

Current alternative is

```
...
If x = 0 Then
...
If False Then
...
...
End If
End If
```

which require more work and attention