Store FQN in CurrentFunction?

[quasilyte]

Right now ClassParseState.CurrentFunction stores only a partial (base) function name instead of FQN.

It's probably more useful to store FQN there.

Since we store method names there as well, it might be a good time to move that to the CurrentMethod field? We can't store method FQN in a way that is useful for us.

This needs some research on how CurrentFunction is used. It should be trivial to get the base name out of the FQN when it's needed.