[adapters] move class EntityAdapter from cubicweb.view to cubicweb.entity
The adapter mechanism is not specific to the use of views. Moving the
class the cubicweb.entity makes this clearer.
3.28
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Changes
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- the class cubicweb.view.EntityAdapter was moved to cubicweb.entity.EntityAdapter
a deprecation warning is in place, but please update your source code accordingly.