Misleading preprocessor specification with mandatory whitespace.

Following this specification as seen in here: https://github.com/dotnet/csharplang/blob/master/spec/lexical-structure.md
For preprocessor directive it is specified that this is the specification:
```
pp_if_section
: whitespace? '#' whitespace? 'if' whitespace pp_expression pp_new_line conditional_section?
;
```

This must mean that something like:
`#if(ANDROID) && !(WINDOWS)`
Should not be correct as '(' is not defined in whitespace, which is mandatory in the specification:
```
whitespace
: ''
| ''
| ''
| ''
;
```

However this will pass in the .NET compiler.

So it seems like an `: whitespace? '#' whitespace? 'if'` can be followed by a '!', '(' or a whitespace.