V2 - make all parcel methods that just access data with no args as getters

[dxinteractive]

Such as parcel.size() -> parcel.size, parcel.isFirst() -> parcel.isFirst etc.
Friendlier for destructuring, and the dev doesn't need to guess which things are access like this or this(). It does close off the possibility for non-breakingly accepting 1 or more args in future, but it's mature enough that I don't think that's an issue.