grammar organization for WDL {1.1,1.2,development}

[mlin]

We have some tech debt organizing the Lark grammars for WDL 1.1 and development:

miniwdl/WDL/_grammar.py

Lines 501 to 505 in 7f3068f

	# For now we're defining 1.1 as 'development minus Directory and multi-line strings' (the
	# subtractions enforced in _parser.py).
	# We'll need to fork them when the development grammar diverges further.
	versions["1.1"] = versions["development"]
	keywords["1.1"] = keywords["development"]

We need a better strategy now that we want to introduce WDL 1.2 formally, while keeping both WDL 1.1 and a future development version.