Convert panoseDefault to namespace object

[NightFurySL2001]

Fix #3197

[anthrotype]

I'd rather use the OS2 table module's Panose object which is used when decompiling or loading from XML. Just add an __init__ to that takes keyword-only arguments and initializes all self attributes to zeros, then fontBuilder can just use_panoseDefaults=Panose().

fonttools/Lib/fontTools/ttLib/tables/O_S_2f_2.py

Line 27 in 3235454

class Panose(object):

If one wishes to override any panose attributes when building OS/2 with fontBuilder they can pass the latter a Panose instance, and can easily construct one with the new constructor.

[anthrotype]

a little test in fontBuilder_test.py would be nice too, e.g. constructing OS/2 once without overriding panose defaults, and another overriding with custom Panose instance, asserting the panose attribute is an object with expected attrs

[anthrotype]

no, I don't think setupOS2 works like that, you want to construct a panose = Panose(**panoseValues) instance beforehand, and pass that one to fb.setupOS2(panose=panose)

[anthrotype]

you are not using these pytest fixture arguments, just define it as def test_setupPanose():