[FIR] Reproduce one more failure for KT-65972 #2

And refactor another related test to
explain the desired behavior.

^KT-65972

compiler/testData/diagnostics/tests/override/intersectionOverridesIntersection.kt

@@ -1,21 +1,36 @@
 // FIR_IDENTICAL
 
-// inherits accept from FirDeclarationStatusImpl and FirResolvedDeclarationStatus
-class FirResolvedDeclarationStatusImpl : FirDeclarationStatusImpl(), FirResolvedDeclarationStatus
-
-// inherits accept from FirElement and FirDeclarationStatus
-open class FirDeclarationStatusImpl : FirPureAbstractElement(), FirDeclarationStatus
-
-abstract class FirPureAbstractElement : FirElement
-
-interface FirResolvedDeclarationStatus : FirDeclarationStatus {
-    override fun accept() {}
+interface FirElement {
+    fun accept() {}
 }
 
+// Provides `FirElement::accept`, because has no override for it
+abstract class FirPureAbstractElement : FirElement
+
 interface FirDeclarationStatus : FirElement {
     override fun accept() {}
 }
 
-interface FirElement {
-    fun accept() {}
-}
+interface FirResolvedDeclarationStatus : FirDeclarationStatus {
+    override fun accept() {}
+}
+
+// IDEALLY:
+//     Provides `FirDeclarationStatus::accept`, because interits
+//     `FirElement::accept` and `FirDeclarationStatus::accept`,
+//     and the latter subsumes the former.
+// REALLY:
+//     Contains an IO, which is an override. So, unlike `FirPureAbstractElement`,
+//     this class does have some override. We make sure this IO is green Kotlin
+//     by calculating `nonSubsumed()` for the base functions
+open class FirDeclarationStatusImpl : FirPureAbstractElement(), FirDeclarationStatus
+
+// IDEALLY:
+//     Provides `FirResolvedDeclarationStatus::accept`, because
+//     inherits `FirDeclarationStatus::accept` and `FirResolvedDeclarationStatus::accept`,
+//     and the latter subsumes the former.
+// REALLY:
+//     Inherits `IO FirDeclarationStatusImpl::accept` and `FirResolvedDeclarationStatus::accept`.
+//     Contains an IO for the above 2 functions. To check if this is green, we unwrap the IO in
+//     the base and then check `nonSubsumed()`, thus doing what is written in "IDEALLY".
+class FirResolvedDeclarationStatusImpl : FirDeclarationStatusImpl(), FirResolvedDeclarationStatus