Field annotations are not properly being set for plugin handlers

[dmtsui]

Annotations on fields for functions such as arguments and exceptions are not properly set for plugin usage. in compile/field.go annotations are set on the FieldSpec's Annotation property, but when generating the service request for plugin handlers, annotations for fields are read from the FieldSpec.Type which has no annotations. This leads to an issue of annotations on fields not being available for plugins when they are properly being added to a thrift file.