FIR: refactor delegate unwrapping

Not implemented override checker will use those to pretend to make
delegeted members (before checking similarly pretended fake overrides)

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/scopes/impl/FirDelegatedMemberScope.kt

@@ -9,6 +9,9 @@ import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.declarations.*
+import org.jetbrains.kotlin.fir.isIntersectionOverride
+import org.jetbrains.kotlin.fir.isSubstitutionOverride
+import org.jetbrains.kotlin.fir.originalForSubstitutionOverride
 import org.jetbrains.kotlin.fir.resolve.defaultType
 import org.jetbrains.kotlin.fir.scopes.*
 import org.jetbrains.kotlin.fir.symbols.ConeClassLikeLookupTag
@@ -162,6 +165,35 @@ class DelegatedWrapperData<D : FirCallableDeclaration<*>>(
 var <D : FirCallableDeclaration<*>>
         D.delegatedWrapperData: DelegatedWrapperData<D>? by FirDeclarationDataRegistry.data(DelegatedWrapperDataKey)
 
+inline fun <reified S : FirCallableSymbol<D>, reified D : FirCallableMemberDeclaration<D>> S.unwrapDelegateTarget(
+    subClassLookupTag: ConeClassLikeLookupTag,
+    noinline directOverridden: S.() -> List<S>,
+    firField: FirField,
+    firSubClass: FirClass<*>,
+): D? {
+    val unwrappedIntersectionSymbol = this.unwrapIntersectionOverride(directOverridden) ?: return null
+
+    val callable = unwrappedIntersectionSymbol.fir as? D ?: return null
+
+    val delegatedWrapperData = callable.delegatedWrapperData ?: return null
+    if (delegatedWrapperData.containingClass != subClassLookupTag) return null
+    if (delegatedWrapperData.delegateField != firField) return null
+
+    val wrapped = delegatedWrapperData.wrapped as? D ?: return null
+    val wrappedSymbol = wrapped.symbol as? S ?: return null
+
+    return when {
+        wrappedSymbol.fir.isSubstitutionOverride &&
+                (wrappedSymbol.fir.dispatchReceiverType as? ConeClassLikeType)?.lookupTag == firSubClass.symbol.toLookupTag() ->
+            wrapped.originalForSubstitutionOverride
+        else -> wrapped
+    }
+}
+
+fun <S : FirCallableSymbol<*>> S.unwrapIntersectionOverride(directOverridden: S.() -> List<S>): S? {
+    if (this.fir.isIntersectionOverride) return directOverridden().firstOrNull { it.fir.delegatedWrapperData != null }
+    return this
+}
 
 // From the definition of function interfaces in the Java specification (pt. 9.8):
 // "methods that are members of I that do not have the same signature as any public instance method of the class Object"