Base expression node types on `dataclasses` #544

Job	Run time
Flake8	21s
Flake8	21s
Pytest on Py3.8	40s
Pytest on Py3.8	40s
Pytest on Py3.9	45s
Pytest on Py3.9	45s
Pytest on Py3.x	40s
Pytest on Py3.x	40s
Documentation	44s
Documentation	44s
Tests for downstream project loopy	28m 21s
Tests for downstream project loopy	33m 42s
Tests for downstream project grudge	28m 22s
Tests for downstream project grudge	33m 45s
Tests for downstream project pytential	28m 21s
Tests for downstream project pytential	33m 30s
Tests for downstream project pytato	28m 20s
Tests for downstream project pytato	33m 42s
Pylint	1m 5s
Pylint	1m 5s
	4h 16m 33s

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