Refactor: process mentions of class object

Rename usages that refer to "default object" concept now
Test data file names are left as is

idea/ide-common/src/org/jetbrains/kotlin/idea/codeInsight/ReferenceVariantsHelper.kt

@@ -88,7 +88,7 @@ public class ReferenceVariantsHelper(
 
             val qualifier = context[BindingContext.QUALIFIER, receiverExpression]
             if (qualifier != null) {
-                // It's impossible to add extension function for package or class (if it's class object, expression type is not null)
+                // It's impossible to add extension function for package or class (if it's default object, expression type is not null)
                 qualifier.scope.getDescriptorsFiltered(kindFilter exclude DescriptorKindExclude.Extensions, nameFilter).filterTo(descriptors)  { callType.canCall(it) }
             }
 

idea/ide-common/src/org/jetbrains/kotlin/idea/util/implicitReceiversUtils.kt

@@ -24,7 +24,7 @@ import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import java.util.HashSet
 
 public fun JetScope.getImplicitReceiversWithInstance(): List<ReceiverParameterDescriptor> {
-    // we use a set to workaround a bug with receiver for class object present twice in the result of getImplicitReceiversHierarchy()
+    // we use a set to workaround a bug with receiver for default object present twice in the result of getImplicitReceiversHierarchy()
     val receivers = LinkedHashSet(getImplicitReceiversHierarchy())
 
     val withInstance = HashSet<DeclarationDescriptor>()