FIC: Introduce isFun property for descriptors and proto

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/AbstractSuspendFunctionsLowering.kt

@@ -294,7 +294,8 @@ abstract class AbstractSuspendFunctionsLowering<C : CommonBackendContext>(val co
                 isData = false,
                 isExternal = false,
                 isInline = false,
-                isExpect = false
+                isExpect = false,
+                isFun = false
             ).apply {
                 d.bind(this)
                 parent = irFunction.parent

compiler/ir/backend.common/src/org/jetbrains/kotlin/ir/builders/declarations/declarationBuilders.kt

@@ -26,7 +26,8 @@ fun IrClassBuilder.buildClass(): IrClass {
         startOffset, endOffset, origin,
         IrClassSymbolImpl(wrappedDescriptor),
         name, kind, visibility, modality,
-        isCompanion = isCompanion, isInner = isInner, isData = isData, isExternal = isExternal, isInline = isInline, isExpect = isExpect
+        isCompanion = isCompanion, isInner = isInner, isData = isData, isExternal = isExternal,
+        isInline = isInline, isExpect = isExpect, isFun = isFun
     ).also {
         wrappedDescriptor.bind(it)
     }