Now FE IR -> BE IR transformation is performed in multiple stages
controller by Fir2IrConverter. Stages are
* files & classes registration
* supertypes & type parameters handling
* functions & properties signature generation
* body generation
After each step we have guarantee (with exception of local classes &
type inference combination, and external symbols) that required symbols
(class/function/property/variable/type parameter)
are already bound to real declarations and have correct parents.
This commit also fixes incorrect parents for local classes
re-ordering the lowering phases.
The changes in InterfaceLowering are necessary so that IrElements that
target the removed functions are re-targeted to the new functions in
DefaultImpls. This affects local functions in interface functions since
now LocalDeclarationsLowering comes before InterfaceLowering.
Mikhail Glukhikh