@validates_schema does not work with @use_kwargs

**@validates_schema** does not work with **@use_kwargs** when there is a property in my schema which is as follow:
```python
@property
def fields_dict(self):
return self._declared_fields
```

do we have some way around for this? I need both to work at the same time.
@jmcarp

Start by reproducing the interaction between @validates_schema and @use_kwargs with a schema defining the shown fields_dict property. Trace how flask-apispec processes the schema and validation decorators; done means both decorators work together for this schema, with a regression test covering the property.

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