Assigning a whole @Struct aggregate embeddable in an UPDATE throws FeatureNotSupportedException.

Repro:

  update ItemWithNestedValue set nested = null
  update ItemWithNestedValue set nested = :value

Observed:

  FeatureNotSupportedException: Update assignment value for field path [nested] is not supported

Required: emit a $set of the entire sub-document for the struct column.

Out of scope for HIBERNATE-93 (path expressions into structs).