Allow omission of either or both ends of Format 2 ranges to indicate -Infinity and Infinity

[Hoolean]

This would match Designspace 5 and otBuilder:

https://fonttools.readthedocs.io/en/latest/designspaceLib/xml.html#label-element-axis

https://github.com/fonttools/fonttools/blob/cdfac571ac70746f47f527328f8bc8eebc0aba9d/Lib/fontTools/otlLib/builder.py#L2762-L2764