#2855 Add a parameter for formatContentModel to allow auto detection of new/removed entities

[JiuqingSong]

Now we can let editor (EntityPlugin) to auto detect changed entity (added, removed) during formatContentModel.

To do this, set context.autoDetectChangedEntities to be true:

editor.formatContentModel((model, context)=>{
 ... // add or remove entities
 context.autoDetectChangedEntities = true;

 return true;
});

Then there will be code to search all changed entities and trigger entityOperation event for each of them.

But if possible, you can still use context.newEntities and context.deletedEntities to manually specify changed entities since they have better performance. Once autoDetectChangedEntities is set to true, context.newEntities and context.deletedEntities will be ignored.