[ion] Ion type annotations not written for scalar and list types on serialization

[mcliedtke]

Creating an issue based on the Google Groups discussion.

Issue: Ion type annotations are not written when using IonAnnotationTypeSerializer. This is due to un-implemented writeTypePrefixForScalar and writeTypePrefixForArray methods in the class.

Will see if I can work on a PR, with tests, for the fix.

[cowtowncoder]

Quick note here: I decided to do a significant rewrite of type id write methods, and this gives more control to actual JsonGenerator subtype. I hope this helps in handling this better, for 2.9.0.

[mcliedtke]

The refactoring done resolved the original issue. Confirmed through tests added in this PR: #109