Harmonize JSONB / JAXB TypeAdapter behavior for Collections

JSONB type adapter logic differs from JAXB in an important way for collections.

In JAXB when applied to a collection an `XmlJavaTypeAdapter` is applied to each entry in the collection.
_whereas_
In JSONB when applied to a collection an `JsonbTypeAdapter` is applied to the Collection as a whole.

The JAXB strategy leads to a simpler code base as only the object in question requires a transformer and the same transformer can be applied to a single field or a collection.
The JSONB strategy requires separate adapters for single instances and for collections.

This request is that the JsonbTypeAdapter processor is adjusted to also recognize collections. For example:

Example class code:
```java
@JsonbTypeAdapter(JsonMyObjectAdapter.class)
private Collection myObjects;
```

Current JSONB adapter code pattern:
```java
public class JsonMyObjectAdapter implements JsonbAdapter, String> {
...
```

Desired JSONB adapter code pattern:
```java
public class JsonMyObjectAdapter implements JsonbAdapter {
...
```

Start by locating the JsonbTypeAdapter processor and tracing how it handles collection-valued fields; compare that behavior with JAXB's XmlJavaTypeAdapter semantics. Verify the change with coverage for adapters on individual objects and collection elements, and consider the work done when the collection example uses a MyObject adapter for each entry without breaking single-value adapters.

Written by the indexing model from the issue text.