Generate parser from `cwltool` extensions #955

Job	Run time
CI linters via Tox (lint-readme)	19s
cwl-utils release test	2m 3s
CI linters via Tox (pydocstyle)	15s
CI tests via Tox (3, 9, lint)	21s
CI tests via Tox (3, 9, unit)	1m 51s
CI tests via Tox (3, 9, bandit)	33s
CI tests via Tox (3, 9, mypy)	1m 2s
CI tests via Tox (3, 10, lint)	21s
CI tests via Tox (3, 10, unit)	2m 10s
CI tests via Tox (3, 10, bandit)	31s
CI tests via Tox (3, 10, mypy)	1m 2s
CI tests via Tox (3, 11, lint)	19s
CI tests via Tox (3, 11, unit)	2m 4s
CI tests via Tox (3, 11, bandit)	21s
CI tests via Tox (3, 11, mypy)	54s
CI tests via Tox (3, 12, lint)	17s
CI tests via Tox (3, 12, unit)	2m 19s
CI tests via Tox (3, 12, bandit)	24s
CI tests via Tox (3, 12, mypy)	1m 2s
CI tests via Tox (3, 13, lint)	29s
CI tests via Tox (3, 13, unit)	2m 17s
CI tests via Tox (3, 13, bandit)	35s
CI tests via Tox (3, 13, mypy)	1m 16s
	22m 45s

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