Generate synthetic functions for local functions with default values, by

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.

compiler/testData/codegen/box/functions/localFunctions/kt3978_2.kt

@@ -0,0 +1,12 @@
+class C() {
+    fun box(): Int {
+        fun local(i: Int = 1): Int {
+            return i
+        }
+        return local()
+    }
+}
+
+fun box(): String {
+    return if (C().box() != 1) "fail" else "OK"
+}