fix(module:code-editor): only emit update if value changed (#5933)

Before notifying Angular (through the ControlValueAccessor mechanism) of a change to
the value we make sure that the value has actually changed. This is necessary to
avoid feedback loops as writeValue (model -> view) would otherwise cause this to be
fired (view -> model) which can cause infinite loop issues on the usage side or
broken validation detection.

fixes #5869

components/code-editor/code-editor.component.ts

@@ -248,6 +248,12 @@ export class NzCodeEditorComponent implements OnDestroy, AfterViewInit {
   }
 
   private emitValue(value: string): void {
+    if (this.value === value) {
+      // If the value didn't change there's no reason to send an update.
+      // Specifically this may happen during an update from the model (writeValue) where sending an update to the model would actually be incorrect.
+      return;
+    }
+
     this.value = value;
     this.onChange(value);
   }