Indicate when the right side (JSON) and left side (FSH) editors are out of sync

[mint-thompson]

Transferred from internal JIRA issue originally created 2021-03-24.

When you edit the text in one side of FSH Online, the other side will become out of sync with it. It might be helpful to have an indication of when this happens.

The initial implementation can just indicate any time it has changed and not worry about if it is changed back to an equivalent state. So if you edit something and change it back, we can leave the indication showing. If this ends up being confusing, we can add another task to do the smarter evaluation and remove the flag.