Generate parser from `cwltool` extensions (#337) #988

Job	Run time
CI linters via Tox (lint-readme)	19s
CI linters via Tox (pydocstyle)	19s
CI tests via Tox (3, 9, lint)	18s
cwl-utils release test	5m 26s
CI tests via Tox (3, 9, unit)	1m 57s
CI tests via Tox (3, 9, bandit)	26s
CI tests via Tox (3, 9, mypy)	55s
CI tests via Tox (3, 10, lint)	18s
CI tests via Tox (3, 10, unit)	2m 5s
CI tests via Tox (3, 10, bandit)	30s
CI tests via Tox (3, 10, mypy)	55s
CI tests via Tox (3, 11, lint)	18s
CI tests via Tox (3, 11, unit)	1m 57s
CI tests via Tox (3, 11, bandit)	20s
CI tests via Tox (3, 11, mypy)	45s
CI tests via Tox (3, 12, lint)	22s
CI tests via Tox (3, 12, unit)	2m 43s
CI tests via Tox (3, 12, bandit)	28s
CI tests via Tox (3, 12, mypy)	50s
CI tests via Tox (3, 13, lint)	24s
CI tests via Tox (3, 13, unit)	2m 19s
CI tests via Tox (3, 13, bandit)	35s
CI tests via Tox (3, 13, mypy)	1m 2s
	25m 31s

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