dataclass import alias for export

[samuelcolvin]

Related issue number

fix #781

Checklist

• Unit tests for the changes exist
• Tests pass on CI and coverage remains at 100%
• Documentation reflects the changes where applicable
• changes/<pull request or issue id>-<github username>.rst file added describing change
  (see changes/README.md for details)

[codecov]

Codecov Report

Merging #783 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #783   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          16     16           
  Lines        2775   2778    +3     
  Branches      553    553           
=====================================
+ Hits         2775   2778    +3

Impacted Files	Coverage Δ
pydantic/dataclasses.py	100% <ø> (ø)	⬆️
pydantic/error_wrappers.py	100% <ø> (ø)	⬆️
pydantic/main.py	100% <100%> (ø)	⬆️
pydantic/typing.py	100% <100%> (ø)	⬆️
pydantic/schema.py	100% <100%> (ø)	⬆️

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