[Builder] familyName entry doesn't call fontmake's family-name argument anymore

[RosaWagner]

Before, the familyName entry in the config.yaml file was used to create subfamilies defined with their dedicated instances in the glyphs file.
Eg: LexendDeca[wght].ttf in https://github.com/googlefonts/lexend
Now it doesn't work, it only builds the main VF.

[RosaWagner]

Otherwise I see these new argument in the doc: fvarInstanceAxisDflts but no additional instruction on how to use it.
Or this argument extraFontmakeArgs could work too?
(asking cause whatever I try doesn't work)

If trying to export a condensed subfamily, using the recipe thing, the operation ends in a font called 'My Font Condensed' but the instances in the fvar are wdth=100 and not 75

- operation: buildVariable
    args: --family-name 'My Font Condensed'

what "works" is this, but I find it a bit complicated:

recipe:
  ../fonts/variable/MyFontCondensed[slnt,wdth,wght].ttf:
    - source: MyFont.glyphs
    - operation: exec
      exe: fontmake
      args: -g MyFont.glyphs --family-name 'My Font Condensed' -o variable  --output-path ../fonts/variable/MyFontCondensed[slnt,wdth,wght].ttf
  ../fonts/variable/MyFontCondensed[slnt,wght].ttf:
    - source: ../fonts/variable/MyFontCondensed[slnt,wdth,wght].ttf
    - operation: subspace
      axes: wdth=75

Then I would need to splitItalic, but no idea how to do that within the recipe thing.

[RosaWagner]

It could be that this is related to #1042, I am trying to include some condensed styles in the fvar (as a workaround) but the builder only includes weight instances and ignore the rest…