In reality plugin key was used only in two ways:
- found corresponding generator for member scope of generated class
- pass it to declaration origin so it can be read in backend IR plugin
Because of first usage plugin key was required to be an object, which
reduces functionality of second usage, because there was no way to
pass any additional info via key to IR (in future this usecase will be
covered with IR declaration attributes, but right now we don't have
them)
So now generator which created some class is now saved in its attributes
and plugins can use any keys they want. And since there is no other
usages of `FirExtension.key` it removed from FirExtension API at all
Dmitriy Novozhilov
c46e9943cc