FIR: deserialize the fun interface flag

compiler/fir/fir-deserialization/src/org/jetbrains/kotlin/fir/deserialization/ClassDeserialization.kt

@@ -69,6 +69,7 @@ fun deserializeClassToSymbol(
         isData = Flags.IS_DATA.get(classProto.flags)
         isInline = Flags.IS_INLINE_CLASS.get(classProto.flags)
         isExternal = Flags.IS_EXTERNAL_CLASS.get(classProto.flags)
+        isFun = Flags.IS_FUN_INTERFACE.get(classProto.flags)
     }
     val isSealed = modality == Modality.SEALED
     val annotationDeserializer = defaultAnnotationDeserializer ?: FirBuiltinAnnotationDeserializer(session)

compiler/testData/compileKotlinAgainstKotlin/useDeserializedFunInterface.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // !LANGUAGE: +NewInference +FunctionalInterfaceConversion +SamConversionPerArgument +SamConversionForKotlinFunctions
 
 // FILE: A.kt