[JS IR] Do not copy interface method if base class inherits it

^KT-58599 Fixed

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/dce/UsefulDeclarationProcessor.kt

@@ -166,7 +166,9 @@ abstract class UsefulDeclarationProcessor(
 
     protected open fun processSimpleFunction(irFunction: IrSimpleFunction) {
         if (irFunction.isFakeOverride) {
-            irFunction.resolveFakeOverride()?.enqueue(irFunction, "real overridden fun", isContagious = false)
+            irFunction.overriddenSymbols.forEach {
+                it.owner.enqueue(irFunction, "overridden by a useful fake override", isContagious = false)
+            }
         }
     }
 

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/JsClassGenerator.kt

@@ -257,7 +257,14 @@ class JsClassGenerator(private val irClass: IrClass, val context: JsGenerationCo
     }
 
     private fun IrClass.shouldCopyFrom(): Boolean {
-        return isInterface && !isEffectivelyExternal()
+        if (!isInterface || isEffectivelyExternal()) {
+            return false
+        }
+
+        // Do not copy an interface method if the interface is already a parent of the base class,
+        // as the method will already be copied from the interface into the base class
+        val superIrClass = baseClass?.classOrNull?.owner ?: return true
+        return !superIrClass.isSubclassOf(this)
     }
 
     private fun generateMemberFunction(declaration: IrSimpleFunction): Pair<JsName, JsFunction?> {
@@ -477,4 +484,4 @@ class JsIrClassModel(val klass: IrClass) {
 class JsIrIcClassModel(val superClasses: List<JsName>) {
     val preDeclarationBlock = JsCompositeBlock()
     val postDeclarationBlock = JsCompositeBlock()
-}
+}