Generate parser from `cwltool` extensions #949

Job	Run time
CI linters via Tox (lint-readme)	1s
CI tests via Tox (3, 9, lint)	1s
CI linters via Tox (pydocstyle)	1s
cwl-utils release test	21s
CI tests via Tox (3, 9, unit)	1s
CI tests via Tox (3, 9, bandit)	1s
CI tests via Tox (3, 9, mypy)	1s
CI tests via Tox (3, 10, lint)	20s
CI tests via Tox (3, 10, unit)	34s
CI tests via Tox (3, 10, bandit)	29s
CI tests via Tox (3, 10, mypy)	24s
CI tests via Tox (3, 11, lint)	25s
CI tests via Tox (3, 11, unit)	18s
CI tests via Tox (3, 11, bandit)	32s
CI tests via Tox (3, 11, mypy)	33s
CI tests via Tox (3, 12, lint)	5s
CI tests via Tox (3, 12, unit)	1s
CI tests via Tox (3, 12, bandit)	5s
CI tests via Tox (3, 12, mypy)	1s
CI tests via Tox (3, 13, lint)	1s
CI tests via Tox (3, 13, unit)	1s
CI tests via Tox (3, 13, bandit)	1s
CI tests via Tox (3, 13, mypy)	1s
	4m 18s

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