Generate parser from `cwltool` extensions #953

Job	Run time
cwl-utils release test	2m 26s
CI tests via Tox (3, 9, lint)	37s
CI tests via Tox (3, 9, unit)	1m 59s
CI linters via Tox (lint-readme)	21s
CI tests via Tox (3, 9, bandit)	36s
CI linters via Tox (pydocstyle)	15s
CI tests via Tox (3, 9, mypy)	55s
CI tests via Tox (3, 10, lint)	20s
CI tests via Tox (3, 10, unit)	2m 11s
CI tests via Tox (3, 10, bandit)	34s
CI tests via Tox (3, 10, mypy)	2m 13s
CI tests via Tox (3, 11, lint)	25s
CI tests via Tox (3, 11, unit)	2m 5s
CI tests via Tox (3, 11, bandit)	27s
CI tests via Tox (3, 11, mypy)	47s
CI tests via Tox (3, 12, lint)	16s
CI tests via Tox (3, 12, unit)	2m 7s
CI tests via Tox (3, 12, bandit)	24s
CI tests via Tox (3, 12, mypy)	59s
CI tests via Tox (3, 13, lint)	31s
CI tests via Tox (3, 13, unit)	2m 16s
CI tests via Tox (3, 13, bandit)	35s
CI tests via Tox (3, 13, mypy)	1m 2s
	24m 21s

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