Support more eager decomposition of transforms OR alter fontmake-py

[rsheeter]

@anthrotype notes:

This optional filter is more eager than our current implementation in fontc. This one will decompose any transformed components anywhere, not just those components that have different 2x2 in different masters like we currently do. We could add an option to do the former (off by default because fontmake doesn't enable this by default).

#288 (comment)

Alternately, update fontmake and gftools to support matching the fontc behavior.

[anthrotype]

the fontc behavior is arguably the most correct of the three. By default we should only decompose transformed components that have different 2x2 transforms between masters. Right now I think fontmake/ufo2ft will let them pass through but varLib will issue a logging warning about the components not being interpolation compatible and leave their gvar blank.. not super nice.
Decomposing all transformed components may be desirable if one wants to support some legacy environment that doesn't play well with those, but is not strictly necessary to support normal VF builds, hence I think it should not be done by default.

[anthrotype]

Right now I think fontmake/ufo2ft will let them pass through but...

No I'm wrong actually, this has been fixed by Simon relatively recently (in ufo2ft v2.31.0), see googlefonts/ufo2ft#698

so I don't think we need to change anything in fontmake-py, the current defaults are as expected there.
Only if we want to match gftools default behavior of decomposing unconditionally all transformed components we need to add a corresponding option to fontc.