Previously, creating a declaration with Fir2IrCallableDeclarationsGenerator/
Fir2IrClassifiersGenerator didn't guarantee that this declaration will
be actually added to the list of parent class/file declarations, which
lead to situations when FIR2IR created some declarations in the air
(mostly fake-overrides)
Before this commit we initialized delegate fields in primary constructor,
that could provoke NPE in case delegate is used in initializer of
some property backing field.
Now we initialize delegate fields directly instead.
Dmitriy Novozhilov