update backing field references when renaming Kotlin property

#KT-7905 Fixed

compiler/light-classes/src/org/jetbrains/kotlin/asJava/KotlinLightField.java

@@ -182,4 +182,9 @@ public abstract class KotlinLightField<T extends JetDeclaration, D extends PsiFi
         }
         return super.isEquivalentTo(another);
     }
+
+    @Override
+    public boolean isWritable() {
+        return getOrigin().isWritable();
+    }
 }

compiler/light-classes/src/org/jetbrains/kotlin/asJava/LightClassUtil.java

@@ -174,6 +174,34 @@ public class LightClassUtil {
         return extractPropertyAccessors(property, getterWrapper, setterWrapper);
     }
 
+    @Nullable
+    private static PsiField getLightClassBackingField(JetDeclaration declaration) {
+        PsiClass psiClass = getWrappingClass(declaration);
+        if (psiClass == null) {
+            return null;
+        }
+
+        if (psiClass instanceof KotlinLightClass) {
+            JetClassOrObject origin = ((KotlinLightClass) psiClass).getOrigin();
+            if (origin instanceof JetObjectDeclaration && ((JetObjectDeclaration) origin).isCompanion()) {
+                JetClass containingClass = PsiTreeUtil.getParentOfType(origin, JetClass.class);
+                if (containingClass != null) {
+                    PsiClass containingLightClass = getPsiClass(containingClass);
+                    if (containingLightClass != null) {
+                        psiClass = containingLightClass;
+                    }
+                }
+            }
+        }
+
+        for (PsiField field : psiClass.getFields()) {
+            if (field instanceof KotlinLightField && ((KotlinLightField) field).getOrigin() == declaration) {
+                return field;
+            }
+        }
+        return null;
+    }
+
     @NotNull
     public static PropertyAccessorsPsiMethods getLightClassPropertyMethods(@NotNull JetParameter parameter) {
         return extractPropertyAccessors(parameter, null, null);
@@ -315,9 +343,11 @@ public class LightClassUtil {
                     getterWrapper = wrapper;
                 }
             }
+
         }
 
-        return new PropertyAccessorsPsiMethods(getterWrapper, setterWrapper);
+        PsiField backingField = getLightClassBackingField(jetDeclaration);
+        return new PropertyAccessorsPsiMethods(getterWrapper, setterWrapper, backingField);
     }
 
     @NotNull
@@ -341,9 +371,10 @@ public class LightClassUtil {
     public static class PropertyAccessorsPsiMethods implements Iterable<PsiMethod> {
         private final PsiMethod getter;
         private final PsiMethod setter;
+        private final PsiField backingField;
         private final Collection<PsiMethod> accessors = new ArrayList<PsiMethod>(2);
 
-        PropertyAccessorsPsiMethods(@Nullable PsiMethod getter, @Nullable PsiMethod setter) {
+        PropertyAccessorsPsiMethods(@Nullable PsiMethod getter, @Nullable PsiMethod setter, @Nullable PsiField backingField) {
             this.getter = getter;
             if (getter != null) {
                 accessors.add(getter);
@@ -353,6 +384,8 @@ public class LightClassUtil {
             if (setter != null) {
                 accessors.add(setter);
             }
+
+            this.backingField = backingField;
         }
 
         @Nullable
@@ -365,6 +398,11 @@ public class LightClassUtil {
             return setter;
         }
 
+        @Nullable
+        public PsiField getBackingField() {
+            return backingField;
+        }
+
         @NotNull
         @Override
         public Iterator<PsiMethod> iterator() {