Move the "optional" attribute from TypeReference to Parameter

[RomainMuller]

The specification models the optional attribute of parameters on their TypeReference instead of directly on the parameter. This creates a confusion between nullable and optional.

The specification needs to be modified so optional parameters carry an optional attribute, while TypeReferences carry a nullable attribute.

Related: #230 #284 #295

[rix0rrr]

So I wanted a function like such:

method(anchor: Construct | undefined, realParameter: string, optionalParameter?: string) {
}

Because that method order made most sense (and yet we didn't necessarily have the first argument always available), but this was rejected.

I've had to reorder arguments, which is not a BIG deal but it was suboptimal to my mind.

[eladb]

@rix0rrr I think is a different issue than where we model optionality of parameters. This is basically about nullibility of parameters, which is currently not supported by jsii (and should in my mind). Care to raise a separate issue?

[rix0rrr]

Isn't adding type nullability something that we need to tackle as part of solving this ticket anyway?

[eladb]

it’s a related topic but not the same. This issue is basically just a modeling improvement (move the “optional” indication from the type reference to the parameter/property specification). Nullability is a different attribute of type references which is not the same as optionality.

If at all, nullability should be part of the type-reference while optionality should be part of the consuming specification.