FIC: Introduce isFun property for descriptors and proto

compiler/frontend/src/org/jetbrains/kotlin/psi/synthetics/SyntheticClassOrObjectDescriptor.kt

@@ -82,6 +82,7 @@ class SyntheticClassOrObjectDescriptor(
     override fun isInline() = false
     override fun isExpect() = false
     override fun isActual() = false
+    override fun isFun() = false
 
     override fun getCompanionObjectDescriptor(): ClassDescriptorWithResolutionScopes? = null
     override fun getTypeConstructor(): TypeConstructor = typeConstructor

compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/descriptors/LazyClassDescriptor.java

@@ -86,6 +86,7 @@ public class LazyClassDescriptor extends ClassDescriptorBase implements ClassDes
     private final boolean isInline;
     private final boolean isExpect;
     private final boolean isActual;
+    private final boolean isFun;
 
     private final Annotations annotations;
     private final Annotations danglingAnnotations;
@@ -158,6 +159,8 @@ public class LazyClassDescriptor extends ClassDescriptorBase implements ClassDes
         this.isExpect = modifierList != null && PsiUtilsKt.hasExpectModifier(modifierList) ||
                         containingDeclaration instanceof ClassDescriptor && ((ClassDescriptor) containingDeclaration).isExpect();
 
+        this.isFun = modifierList != null && PsiUtilsKt.hasFunModifier(modifierList);
+
         // Annotation entries are taken from both own annotations (if any) and object literal annotations (if any)
         List<KtAnnotationEntry> annotationEntries = new ArrayList<>();
         if (classOrObject != null && classOrObject.getParent() instanceof KtObjectLiteralExpression) {
@@ -533,6 +536,11 @@ public class LazyClassDescriptor extends ClassDescriptorBase implements ClassDes
         return isActual;
     }
 
+    @Override
+    public boolean isFun() {
+        return isFun;
+    }
+
     @NotNull
     @Override
     public Annotations getAnnotations() {