The only case we may need fake override for private members is
a situation when class refers itself with different type arguments.
So in this commit we forbid such fake overrides when we can prove
that class does not refers itself here.
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