Improve transition to large size in IonStructLite

[tgregg]

transitionToLargeSize is called only in IonContainerLite.nextSize, and the call_transition boolean there is always true. transitionToLargeSize has only one non-trivial implementation, in IonStructLite, and that implementation ignores the input size.

If we bleed field name concerns into IonValue, why not bleed field map concerns into IonContainerLite? transitionToLargeSize could be renamed fieldMapIsActive and used all the same. Or transitionToLargeSize could call fieldMapIsActive.

Alternatively, it might bear a little more looking at IonContainerLite.nextSize and the IonStructLite interactions to see whether nextSize really does need to ensure this property. Does it, really, if the field map is lazy and this property is ensured wherever it may need access? Perhaps we can do away with transitionToLargeSize entirely.

Originally posted by @jobarr-amzn in https://github.com/amazon-ion/ion-java/pull/557#discussion_r1320211875

We now have logic in IonStructLite to lazily construct the field map. We should explore eliminating transitionToNextSize, which is called when elements are added, in favor of only lazy construction. The performance impacts of this on existing use cases would need to be measured.