Represents a function argument in the AST.
@:optionalmeta:Null<Metadata>
The metadata of the function argument.
name:String
The name of the function argument.
@:optionalopt:Null<Bool>
Whether or not the function argument is optional.
type:Null<ComplexType>
The type-hint of the function argument, if available.
@:optionalvalue:Null<Null<Expr>>
The optional value of the function argument, if available.