Handle non-optional nullable type

[nrigaudiere]

Some Web APIs says “This parameter is not optional, but can be set to null”.

jsruntime does not support this for now:

• a nullable parameter (ie. ?<Type>) is translated as an optional parameter
• and if you remove the nullable modifier (ie. <Type>) a null value is not allowed

The easiest way to handle that would be to keep ?<Type> for optional parameter and create custom type for mandatory nullable parameter <NullableType>, eg. NullableNumber or NullableNode.

It’s a bit verbose but we can use a comptime function generator to help with that.

Maybe another solution is possible.