Add JsonFormat.Shape awareness for UUID serialization (UUIDSerializer)

[cowtowncoder]

(note: fix for FasterXML/jackson-dataformats-binary#218)

Although UUID deserializer can read both String and Binary (if available) representations, it is strictly based on capabilities of the backend (see JsonGenerator.canWriteBinaryNatively()), and there is no easy way to override behavior. This can be problematic in general, but caused issues in particular with Avro format which had formerly claimed it can not write binary natively: issues was fixed for 2.11, but some existing code/models were already counting on String-based representation.