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.
Current implementation of calls with super qualifier relies on
invokespecial, which has some more constraints than regular virtual
invocations. When those constraints aren't met, accessors are needed.